Child's Toy

A child's toy consists of three cars that are pulled all in a row
on small frictionless wheels. The cars have masses m_{1}=3.1kg,k_{2}=2.4kg,m_{3}=1.2kg.
If they are pulled to the right with a horizontal force P=6.5N, find

a) the acceleration of the system

b) the force exerted by the second car on the third car

c) the force exerted by the first car on the second car.