I do not understand this question

B) The maximum height is 11.3 ft and it reaches this height at 0.72 seconds.

Explanation:
Part (a) : getting the time taken to reach maximum height:
The given equation is:
h = -16t² + V0*t + h0

We are given that:
Initial velocity (V0) =23 ft/sec
Initial height (h0) = 3 ft

The equation now becomes:
h = -16t² + 23t + 3

For maximum height:
dh / dt = zero
This means that:
-16(2) t + 23 = 0
-32t + 23 = 0
32t = 23
t = 0.71875 sec which is approximately 0.72 seconds

Part (b): getting the maximum height:
The equation given to get the height is:
h = -16t² + V0*t + h0

We are given that:
Initial velocity (V0) =23 ft/sec
Initial height (h0) = 3 ft

We have calculated that:
time taken to reach maximum height = 0.72 sec

Substitute with the givens in the equation to get the maximum height as follows:
h = -16t² + V0*t + h0
h = -16(0.72)² + 23(0.72) + 3
h = 11.2656 ft which is approximately 11.3 ft

Hope this helps :)