Answer: $180
Explanation:
a right triangle has three sides: the two smaller ones and the big one. the two smaller ones squared add up to the bigger one squared.
this is the pythagorean theorem, a^2 + b^2 = c^2.
in this case, it would be 9 squared + 12 squared = c squared.
81 + 144 = 225
225 is the square of 15, so the third side is 15.
now, solve for the perimeter.
the perimeter is the 3 sides added up, so 9+12+15 = 36 feet of perimeter.
each foot costs $5, so 36x5= 180.
$180 is the answer.