Simply substitute the 7 in for c in the equation then solve...
17 - 2c =
17 - 2 (7) =
17 - 14 = 3
There is 6 parts in a two column format.
It's N=9 it's really confusing but trust me it N
The sides
12-3a
12-3a
4(2a-5)=8a-40
so for perimeter we + them
(12-3a)+(12-3a)+(8a-40)
=
2a-16
Correct answer is 6... NOT 7...
