So the best way to do this is to simply set h = 0 since the time it hits the ground will be at h = 0, then solve using the quadratic formula. So 0 = -4.9t^2 + 18.9t + 2.8. Now use the quadratic formula. So -18.9 +/- sqrt( 18.9^2 - 4(-4.9)(2.8)) all over -9.8. Now simplify. So (-18.9 +/- 20.3)/(-9.8) = t. So t = 4 seconds. Hope this helps