We are asked when the rocket will strike the ground, so that is the same that sayin when will the rocket's height will be zero again, that is, y=0. so we have to solve
the solutions of this equations are
So, the rocket will strike the ground after 7.3 seconds
Since jason is currently at 54 feet above sea level and David is 11 feet below sea level the add 11 plus 54 which would give you 65 feet is there distance of elevations