Calcualte how many milliliters of carbon dioxide would be produced theoretically from 20g of sucrose of 25 degree C and 1 atmosphere pressure.

I can use the formula PV=nRT

20g C12H22O11 * moles sucrose/342.3g suc.
that would equal: .0584 moles. But what next. The experiment usually is: 1 mole of sucrose yields 4 moles of carbon dioxide. I'm just lost here. Should I just plug in my results into the formula PV=nRT ?

You don't say what you did to get CO2. I assume you burned it. If so this is what you do. Where did you get your 4 mols CO2? Perhaps you did not burn it OR you burned it in insufficient oxygen. Anyway, this will give you to procecure IF it was completely burned.
C12H22O11 + 12O2 ==> 12CO2 + 11H2O

20g sucrose/molar mass = number of mols.
mols sucrose x 12 = mols CO2