If a=4, what is the value of the expression 12-a/4?

11
To find the answer, we're going to need to do some substitution! The problem tells us that a is equal to 4. So, wherever there is an a, you're going to change that to a 4.
12-(4/4)
Now, remember PEMDAS. Parenthesis comes first.
4/4 is equal to 1.
12-1
= 11