Question 956472
The two legs are in a ratio of 9:12=3:4, which means this is a 3-4-5 triangle.
Bruce is on the shorter leg, so he would be at the larger acute angle of 53 degrees. 
ANSWER: He would throw the ball at a 53 degree angle.
If you don't know these angles, find the hypotenuse (5*3=15 feet)
so arcsin(opp/hyp)=arcsin(12/15)=53 degrees.