Question

Combine like terms.

Answer 1

$4a+b+a=5a+b$

Answer 2

To combine these terms you would add up the a's and b's.
4a+b+a is the same as 4a+a+b. Anything without a constant in front has a value of 1. You have 4a's and you need to add another a. That equals 5a's. The b is left alone since you can only add like variables.
The answer would be C) 5a +b