a) speed(horizontal) = distance / time
time to reach plane again = 735/2u
time to reach highest point = 1/2 ( 735/2u )
Uvertical = 3u
Vvertical = 0
t = 1/2 ( 735/2u )
a = -g
a = (V-U)/t
-g = -3u / (183.75/u)
u² = 600.25
u = 24.5
b) time to reach plane again = 735/2u
T = 15 sec
speed² = 49² + (V)²
65² - 49² = V²
V : speed vertical
V² = 1824
V² = U² + 2as
1842 = 5402.25 - 2 x 9.8 x S
S = 181.6 m