Stephanie M. answered 05/02/15
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You want to find t when height is 87. Plug height h = 87 into the formula and rearrange it so everything is on one side:
87 = -16t2 + 195t
0 = -16t2 + 195t - 87
Solve for t using the quadratic formula, where a = -16, b = 195, and c = -87.