Answer:
b = 6 sqrt(2)
Explanation:
Since this is right triangle, we can use the Pythagorean theorem
a^2+b^2 = c^2 where a and b are the legs and c is the hypotenuse
3^2 + b^2 = 9^2
9+b^2 = 81
b^2 = 81-9
b^2 = 72
Take the square root of each side
sqrt(b^2) = sqrt(72)
b = sqrt(36*2)
b = 6 sqrt(2)