32 y/o male - average ht and wt. I have about 45 min to 1 hour each day to work out in the fitness center at my work. I have access to mostly cable machines with very few free weights. For a few months now I have doing the following:

Chest/back 1 day: chest - sitting chest press and flys, back - lat pull downs and rows

Arms/Shoulders 1 day: Single arm iso curls and over the head tricep extensions (triceps with barbell), shoulder press and straight arm extensions.

I alternate back and forth between those 2 for now, usually with days of all cardio in between to break it up, and abs thrown in at the end. No legs for now, recovering from knee surgery.

Question - what type of reps/weight combo should I use to build mass? Right now it's 4 sets of 8/10 of each at about 75%. More weight, less reps? More reps, less weight? Change everything?