Maths help please

Question

In a simulation, the path of a new aircraft after it has achieved weightlessness can be modelled approximately by h(t) = -5t² + 200t+ 9750, where h is the altitude of the aircraft, in metres, and t is the time, in seconds, after weightlessness is achieved. How long does the aircraft take to return to the ground, h(t) = 0? Express your answer to the nearest tenth of a second.

Answer 1

-5t^2 +200t +9750 = 0

t^2 - 40t - 1950 = 0

(t-20)^2 = 1950 + 400

t-20 = sqr2350

t = 20 +48.48

t = about 68.5 seconds to splash down