I have drawn my force body diagrams, but I need help making forming the equation for this problem. Any assistance is greatly appreciated!

A 60 kg block slides along the top of a 100 kg block. The lighter block has an acceleration of 3.8 m/s2 when a horizontal force F= 390 N is applied. Assuming there is no friction between the bottom 100 kg block and the horizontal frictionless surface but there is friction between the blocks. Find the acceleration of the 100 kg block during the time the 60 kg block remains in contact.