c – The function gets two numbers and returns the sum of the even numbers

Can someone help me, I do not know how to continue. Here is the question

• Define the function calculate_pair, which accepts both numbers and returns the number of even numbers.
  that exists between them.
• Define the present_results function, which receives both numbers and the number of even numbers.
  and prints a message like "Between 5 and 10 there are 3 even numbers".
• Create a main program that asks the user for two integers, otherwise
  and a multiple of 3. Ask again until the situation is met.
• Use the main function calculate_pars to calculate the number of even numbers in between
  values. And use the main function in the function present_results.

#include 
#include 

int calcula_pares(int n1,int n2);
int apresenta_resultados(void);

int main(void)
{
    int r, q,n1, n2;
    printf("Insira o primeiro numero: ");
    scanf("%d", &n1);
    printf("Insira o segundo numero: ");
    scanf("%d", &n2);

    r = apresenta_retuntados();
    q = calcula_pares(n1,n2); 

    printf("nn");
    system("pause");
}


int calcula_pares(int n1,int n2)
{
    int i, media;
    for (i=n1; i<=n2/2; i++) {
        printf ("Numero par: %dn",i*2);

    }
    return i;
}

int apresenta_resultados(void)
{
    int j, soma;
    printf("A soma dos resultados eh: ", j);
    return soma;
}