When we have a function and want to evalueate it for some "x", we just substitute every "x" with the value in parenthesis. So, to evaluate f(a + 2), we have x = a + 2, so we need to substitute every "x" in the function with a + 2:
Now, to simplify, we first need to use the distributive property on the second parenthesis and evaluate the binomial in the first:
Now, we group the like-terms and add them:
For yhe other one, Let's do each term and then make the substraction:
So: