Answer:
3 is
Explanation:
A co efficient is when there is a number attached to a variable.
A constant is a number standing by itself.
An expression is the numbers that are being shown in your post (when you have to solve for x, its kind of like an equation but it snot the same *just to give you an idea*).
I just want you to be prepared for middle school because your going to need to know these names ;D