For the next few problems you need to understand what it means to evaluate a function. You simply replace the variable with the number at which you evaluate the function. For example, the answer to the first question below is $15$ since $$15 = 3*3 + 6.$$
Let the function $f$ be defined by $$f(x) = 3 x + 6.$$ Then $f(3) =$ and $f(4) =$