Fill in the missing value for V. P=1.2 atm, n-5.00 and T= 300.15 K....how do I set up the PV=nRT or do I solve in a different way?

What do you mean how do you set it up. Substitute the values given into PV = nRT and solve for V (in L). R is 0.08206 L*atm/mol*K