Answer:
acc to ques....perimeter of figure= 3a^2+15a+9
let missing dimension be x
= x+10a-2+a^2-7+5a=3a^2+15a+9
x+15a+a^2-9=3a^2+15a+9
x=2a^2+18
Factor by grouping
(2x+3) (x-5)
Step-by-step explanation: