What is the acceleration of a falling block attached to a pulley system?

[TG3]

Homework Statement

A block of mass m1 = 2 kg rests on a table with which it has a coefficient of friction µ = 0.75. A string attached to the block passes over a pulley to a block of mass m3 = 4 kg. The pulley is a uniform disk of mass m2 = 0.5 kg and radius 15 cm. As the mass m3 falls, the string does not slip on the pulley.
With what acceleration does m3 fall?

Homework Equations

Frictional Force = mew x normal
F = MA
Newtons' second law

The Attempt at a Solution

If I could treat the pulley as a point and didn't have to pay attention to it this would be a cinch. To be honest, I don't know what to do with it at all, and I'm looking for some conceptual help here.

 

[TG3]

Much time later, I finally got the acceleration to be 3.9. The next question in this set is: what is the tension in the string above the table, and below the pulley. (They will be separate.)
Now, since F=MA, I thought this would be easy. 3.9 x 4 = 15.6. It itsn't that easy, it turns out. Any ideas?

 

[Redbelly98]

Well, 15.6 N is the net force on the 4 kg mass.

This force is due to the string tension and what else?