how to insert an algebraic expression as an input in a function

dear all

i wanna write a function which take an algebric expression and a digit as arguments. then calculate the result of the algebric expression with digit and finally take back the answer. the algebraic expression is " x^2+x" , the digit is "2" and the function is as below:

eq=x^2+x;

function [out]=saeed(eq,2)

now i have 2 problems.

1-the first problem is that should i define x as an symbol?

2-how can i write the function?

thanks alot