Add values from object list columns in Razor

I have a table, where I get the data from a View (SQL Server) and perform some operations on my page. On this page, I have a filter, to display only the pages for the selected year.

Until this part is all correct, along with the filter, such as seen in this example .

The operations are performed, entirely in my View, which follows below:

<table id="item-list" class="item-list table" style="margin-bottom: 0px;" border="1">
    <thead>
        <tr>
            <th rowspan="2">
                Mês
            </th>
            <th rowspan="2">
                Remuneração<br />
                Total R$
            </th>
            <th colspan="4">
                <p align="center">
                    Contribuinte
                </p>
            </th>
            <th colspan="4">
                <p align="center">
                    Município
                </p>
            </th>
        </tr>
        <tr  bgcolor="#ffffff">
            <th>
                %
            </th>
            <th>
                Mês R$
            </th>
            <th>
                Ano R$
            </th>
            <th>
                Acumulado R$
            </th>
            <th>
                %
            </th>
            <th>
                Mês R$
            </th>
            <th>
                Ano R$
            </th>
            <th>
                Acumulado R$
            </th>
        </tr>
    </thead>
    <tbody>
        @*Variáveis para somar os totais dos campos*@
        @{
            double totalContribuinte = 0;
            double totalMunicipio = 0;
        }

        @foreach (var item in Model.Previdencia.GroupBy(g => new {g.NmPessoa, g.dtCompetencia.Value.Year}))
        {
        @*Variáveis para somar os totais dos campos por ano*@
            double subtotalContribuinte = 0;
            double subtotalMunicipio = 0;

            foreach (var contribuicoes in item.ToList())
            {

            @*Realizam as somas dos campos*@
                subtotalContribuinte += contribuicoes.Contribuinte;
                totalContribuinte += contribuicoes.Contribuinte;

                subtotalMunicipio += contribuicoes.BaseCalculo;
                totalMunicipio += contribuicoes.BaseCalculo;

            @*Adiciono a classe igual a selecionada no select*@

                <tr class="@contribuicoes.dtCompetencia.Value.Year" bgcolor="#ffffff">
                    <td align="right">
                        @contribuicoes.dtCompetencia.Value.Month.ToString("00")
                    </td>
                    <td align="right">
                        @contribuicoes.BaseCalculo.ToString("N")
                    </td>
                    <td align="right">
                        11
                    </td>
                    <td align="right">
                        @contribuicoes.Contribuinte.ToString("N")
                    </td>
                    <td align="right">
                        @subtotalContribuinte.ToString("N")
                    </td>
                    <td align="right">
                        @totalContribuinte.ToString("N")
                    </td>

                    <td align="right">
                        11
                    </td>
                    <td align="right">
                        @contribuicoes.BaseCalculo.ToString("N")
                    </td>
                    <td align="right">
                        @subtotalMunicipio.ToString("N")
                    </td>
                    <td align="right">
                        @totalMunicipio.ToString("N")
                    </td>
                </tr>

            }
        }
    </tbody>
</table>

My ViewModel used, with fields:

public class ExtratoPrevidenciaViewModel
    {
        public int Codigo { get; set; }
        public int CdMatricula { get; set; }
        public Int16 SqContrato { get; set; }

        public string NmPessoa { get; set; }

        [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
        public DateTime? dtCompetencia { get; set; }

        public double Contribuinte { get; set; }
        public double Municipio { get; set; }
        public double BaseCalculo { get; set; }

    }

My problem: How to perform the sum of all values, per column, separating by year, how is my GroupBy ?

The expected end result, would look something like this.