College Algebra word problem

Question

A ball is thrown in the air from the top of a building. Its height, in meters above ground, as a function of time, in seconds, is given by h(t) = −4.9t² + 22t + 12.

 How long does it take to reach maximum height? (Round your answer to three decimal places.)

Answer 1

h'(t) = -9.8t +22 = 0

9.8t=22

t=22/9.8 = 11/4.9 = 2.245 seconds

take the function's derivative & set equal to zero, then solve for t