Three Crates

Three crates with masses m_{1}=45.2kg,m_{2}=22.8kg and m_{3}=34.3kg
on a horizontal frictionfigureless surface.

a) What horizontal force F is needed to push the crates to the right,
as one unit, with an acceleration of 1.32m/s^{2}?

b) Find the force exerted by m_{2} on m_{3}.

c) Find the force exerted by m_{1} on m_{2}.