Question

9(a-1) + 4(a-1)

Answer 1

start distributing.
9 times a - 9 times 1 and do the same for the other side

Answer 2

(9a-9)+(4a-4)
(9a+4a)+(-9-4)
13a-13

Answer 3

and then combine like terms

Answer 4

oh ok i understand now