I am really bummed out about this physics class that I am in now. I don't get anything and it is frustrating me to my breaking point. I am trying to do this problem:

A 5.00-kg concrete block rests on a level table. The coefficient of kinetic friction between the block and the table is 0.55. A 4.00-kg weight is attached to the block by a string of negligible mass passed over a light frictionless pulley. What is the acceleration of the block when the 4.00-kg weight is released?

I believe I've set the problem up correctly. When I completed the steps that I knew I was left with three equations:
1. T+Ffrk=5.00-kg*a
2. Fn=49.00N
3. T-39.2N=-5.00-kg*a

From this point on out I am stuck. I dont know which way to turn. Could someone HELP ME PLEASE???