i thought I would add that should you require more outlets and wish to run dedicated lines, you can buy those slimline dual breakers (15 or 20a) like the ones in your pictures on the bottom right, and replace existing non-slimline breakers, just move the existing circuits to 1 of the ports on the slimline and you have the 2nd port to use as you see fit.
you can still run into the problem of tripping your main breaker, which doesnt appear to be in that panel that you show, probably located centrally in the apartments, if you run more amps than that panel is fed with. (I would suspect you have at least a 50 amp breaker feeding you on 8 or 6awg lines (the red and black lines you see screwed into the sub panel on either side of the bottom 2 breakers)
EDIT: on second look, you only have at most some 10awg feeding that panel, which if it was installed to code, can carry 50 amps max. although i wouldnt put more than 30 amps on it at once personally, it will get very hot, and if you dont know that its secure and new wiring in good condition, it can cause a fire at 40-50 amps easily in an older building (15-20 yrs or older)