Answer:
9 ft
Explanation:
The Pythagorean theorem states
a^2+b^2 = c^2 where a and b are the legs and c is the hypotenuse
Substituting in what we know (one leg is 12 and the hypotenuse is 15)
12^2 +b^2 = 15^2
144+ b^2 = 225
Subtract 144 from each side
144-144 +b^2 = 225-144
b^2 =81
Take the square root of each side
sqrt(b^2) = sqrt(81)
b = 9