Use the equation
t = -b / (2a)
where:
a = -16
b = 30.4
Plug these values into the equation.
b)
Evaluate h(t) at the time of maximum height. The time of maximum height is the value found in previous part.
c)
Set h(t) equal to 3 and solve for t.
3 = -16t2 + 30.4t + 5
0 = -16t2 + 30.4t + 2
Solve this quadratic equation for t. I suggest you use the quadratic formula to solve for.