Motion In A Straight Line

Two smooth inclined planes $A$ and $B$ each of height 20 m have angles of inclination $30^{\circ}$ and $60^{\circ}$ respectively. If $t_1$ and $t_2$ are respectively the times taken by two blocks to reach the bottom of the planes $A$ and $B$ from the top, then $t_1-t_2=$ (Acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )