I don't believe you can do that, look up atm basic units, i mean Newton is kg*m/s^2, what is atm equal to? and use the relation above cm^3 = mL, and see if you can follow from that. This problems can be solved by converting to the same types of units, and simple elimination of analogous units.
but i am stuck here, how can i cancel out further units? since the bottom is addition, i have no idea what to do from here...am i still allowed to convert the m^2 to liters and cance it out with the top, as well as the Pa with the atm on top?