Given data:
The expression for the height is h= -16t^2 +vt+c.
The expression for the velocity is,
At t=0, the velocity is 50ft/s.
At t=0, h= 4ft
The expression for h is,
Substitute 10 ft for h in the above expression.
Here, two value of times indicates that one in the ascent and second one in the descent.
Thus, the value of time are 3 seconds and 0.125 s.