Calculate the acceleration of the system

[RedBurns]

Two crates, of mass m1 = 60 kg and m2 = 130 kg, are in contact and at rest on a horizontal surface (Fig. 4-54). A 620 N force is exerted on the 60 kg crate. The coefficient of kinetic friction is 0.15.

(a) Calculate the acceleration of the system.
m/s2 (to the right)
(b) Calculate the force that each crate exerts on the other.
N
(c) Repeat with the crates reversed. acceleration m/s2
crate force N


I'm trying to caculate the acceleration and I can't seem to get it. I tried this but I know it is incorrect:

Mk*G=a

.15 * (60*9.8) - .15 *(130*9.8)= -102.9

Can someone tell me where I'm going astray?

 

[tony873004]

$$\mu_{k} mg$$
is not your acceleration. It is the force exerted by kinetic friction. It opposes the 620 N force applied to the 60 kg crate.