A stop sign has 8 sides and all angles are the same, so it is a regular octagon.
You plug in x for 3 so it would be 10(3) + 2, and 10 times 3 is 30 and 30 plus 2 is 32
If the problem looks like mine, the answer is 152.
A=3
B=4
C=5
Substitute 3 in for 'a' in the equation, and 5 in for 'c' in the equation to get 17.