A ball rolls off a horizontal shelf that is a height h above the floor and takes $0\mathrm{.}5$ s to hit the floor. For the b take $1\mathrm{.}0$ s to reach the floor, the shelf's height above the floor would have to be

a$)$

$2$h$.$

b$)$

$3$h$.$

V$2$h$.$

d$)$

$4$h$.$