Solution

Dik : V_o = -10m/s
h = V_o.t + 1/2.g.t²
= 270 = -15(t) + 1/2(10).t²
= 5 t² - 15 t = 270
so is got t₁ = -6 and t₂ = 9<> = 5 t² - 15 t - 270 = 0 → find the roots of quadratic equations
is got : t₁= -6 (did not meet due to negative) dan t₂=9

With so means bombs falling to the ground after 9 second. In that interval, then the aircraft has also been moved so far
h = v.t
h=15(9)
h=135 m
So, after the bomb hit the ground, the balloon is high : h = 270 + 135 = 405 m.