Hello. I do not know this answer on the spot. But there is an app called mymath and you can download it on any apple or android device that will give you the answer to any of the variables in the equation. Hope it helps
7y+11+7y+11+7y+11=180(A.S.P)
21y+33=180
21y=180-33
21y=147
y=147/21
y=7
y=7
