given the equation:
h = -16t^2 + 129t
we are to find the height of the object after 4 seconds
in other to get the height of the object after 4 seconds is to substitute 4 into the equation.
that means we replace t by 4 in the equation
so,
h = - 16t^2 + 129t
substituting 4 into the equation
h = -16(4)^2 + 129(4)
h = - 16(16) + 516
h = -256 + 516
h =