A 1.5- block rests on top of a 7.5- block. The cord and pulley have negligible mass, and there is…

A 1.5- block rests on top of a 7.5- block. The cord and pulley have negligible mass, and there is no significant friction anywhere.What force must be applied to the bottom block so the top block accelerates to the right at 2.1 m/s^2 ?