Find the maximum heigh reached by the rocket

y=-16x^2+146x+137

The height of the rocket y in feet is related to the time after launch, x in seconds, by the given equation i.e.
(1)
It is required to find the maximum height reached by the rocket. For maximum height put .
So,

Put x = 5.15 in equation (1).

So, the maximum height reached by the rocket is 503.39 m.

7.666270253x10 raised to the 18th power