What does it mean to evaluate an expression in 5th grade

What is the measure of ac? 5 units 13 units 26 units 39 units 3x- 2b 6x + 9

The sum of the first eight terms of an arithmetic progression is 9m + 14. the fifth term of the06 progression is 2m - 6, where m is a constant.given that the first term of the progression is 26,find the value of the common difference, d and thevalue of m.

Factor the polynomial. b^2 + 4b + 4