Question

When will the trampolinist land on the trampoline?

Answer 1

Well it depends on how high did he jump in inches

Answer 2

Since you want to know when the person reaches the trampoline, the height will be zero.
0 = -16t^2 + 60
Solve the quadratic
16t^2 = 60
Divide both sides by 16
t^2 = 60/16
t^2 = 15/4
t = sqrt (15/4)
t = 1.936