*note* This question has been deleted.
You almost said it! The normal force is mg cos(35) (not just mass times sin- mg times cosine-look at your diagram) and the friction force is the coefficient of friction times that. The problem is that, here, you are not given the coefficient of friction- that's the "unknown" you are asked to find. Let's call it "c". The friction force on the 8 kg mass is 8(9.5)cos(35) and for the 3.5 kg mass it is 3.5(8.9)cos(35).I also know the force of friction is equal to the coefficient of friction times the normal force. I think the normal force is mass times the sine of theta times gravity, but I don't know how to find the force of friction.