guys,
I have lost some weight recently - 11kg in 2months.
Have access to gym and can go there for 30-60mins a day.
Want to try and turn remaining fat in to some muscles

mostly in upper part of the body - chest arms and get some extra strength. I would like to strengthen my lower back as well if possible - back = belly muscles ? need to get them in form for sure
should I be doing sets of more reps with lower weights or less reps with heavier weights ?
and what would be best basic exercises for my back ?
need to do plenty sit-ups that's for sure
Gym is pretty new and full of all kinds of machinery
Thanks