Question 40134
In each case, |x + yi| = sqrt(x^2 + y^2), so 
|9-12i| = sqrt(81 + 144) = 15

|15-20i| = sqrt(15^2 + 20^2) = sqrt(625) = 25

|8+15i| = sqrt(64 + 225) = sqrt(289) = 17