what i am trying to figure out is, how can i translate the real world info to ms project.

lets say i have a wall to paint, 400sf. and 1 worker takes 8 hours to paint 100 sf wall, and I am going to use two labors. lets say i know these two things. now i go to my ms project, and
1-enter an activity called "paint wall"
2-assign laborer#1 to it, and then assign laborer#2, each 100%
3-now what? do i enter work? if so do i enter 32 myself? i mean how can i let ms project know, i have 400sf to paint? if i am entering work here, it means i enter 32h? which means i do the calculation myself outside, to find out the amout of time required for one (1) unit and enter it as work? if not how?