500 error in servlet instantiation

Hello.

I'm trying to make a servlet, but tomcat does not find this servlet class. The error is:

  

HTTP Status 500 - Error instantiating servlet class server.PrimeiraQuestao ------------------------------------ --------------------------------------------

Server is the package and FirstQuestao is the class.

The following is the code error for web-app.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <display-name>teds</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>questaoum</servlet-name>
        <servlet-class>servidor.PrimeiraQuestao</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>questaoum</servlet-name>
        <url-pattern>/questaoum</url-pattern>
    </servlet-mapping>

</web-app>