Ned help on a hard projectile motion question!

Two boys are playing in the snow in the diagram below. One boy is standing on the edge of the roof while the other is 3.75 m underneath the first. The boy on the ground runs forward at 5.20 m/s. The boy on the roof can throw a snowball at 8.50 m/s.
(a) At what angle should the boy on the roof throw the snowball so that it hits the running boy on the top of his head?
(b) What distance x did the boy get to?
(c) How long was the snowball in the air?


heres a link to the question, its question 2 and it has a diagram
http://www.kwantlen.bc.ca/science/physic…

Please help, he does not provide answers and i don't know how to approach this question, seems to me its a "chase question so i think you must set constraints and such"

(a).

analyzing for the first boy,

x = vt

x = (5.2)t

t = x/5.2




analyzing for the second one,

x = Vo t cos Φ

t = x/(Vo cos Φ)

x/5.2 = x/(Vo cos Φ)

Vo cos Φ = 5.2

8.5 cos Φ = 5.2

cos Φ = 0.611765

Φ = 52.28°




(b).



y = Vo t sin Φ + ½ g t²

-3.75 = 8.5 t sin 52.28° + ½ (-9.8) t²

choose positive value for t,

t = 1.79784 sec

x = Vo t cos Φ

x = (8.5)(1.79784) cos 52.28°

x = 9.34936 m



(c).

based on the answer at (b) part, t = 1.79784 sec