The height of a football, in feet, t seconds after it is kicked into the air off of a tee, is modeled by the function h(t) = –16t2 + 35t + 0.25. what is the approximate maximum height of the football?

The function is:
f ( t ) = - 16 t² + 35 t + 0.25
We can use the derivative:
f ` ( t ) = - 32 t + 35
- 32 t + 35 = 0
t = 35 : 32 = 1.09375 s
The maximum height is:
f ( 1.09375 ) = - 16 · ( 1.09357 )² + 35 · 1.09357 + 0.25 =
= - 19.14 + 38.28125 + 0.25 = 19.39 ft ≈ 19.4 ft.
The approximate maximum height of the ball is 19.4 ft.

Idon't know what's the answer lol