In Denver, children bring their old jack-olanterns to the top of a tower and compete for accuracy in hitting a target on the ground (Figure $4-15) .$ Suppose that the tower is $9.0 \mathrm{m}$ high and that the bull's-eye is a horizontal distance of $3.5 \mathrm{m}$ from the launch point. If the pumpkin is thrown horizontally, what is the launch speed needed to hit the bull's-eye?