The dump truck body represents the hypotenuse of a right triangle....one leg is 9ft ...this is the leg OPPOSITE of the angle that needs to be at least 50 degrees....
sin x = opposite/hypotenuse
sin x = 9/15 x = asin(9/15) = 36.869897645844 degrees Not high enough yet......
Let's find out how high it needs to be:
sin 50 = x/15 x = 15*(sin(50)) = 11.490666646785 ft