this is just a simple ideal gas law problem. PV=nRT
you are solving for pressure P where:
V= 12L
n= number of moles = 10 moles
R= ideal gas law constant= .0821 (make sure to choose the correct one based on what you are given. Use the one below for Pressure in ATM and volume in L).
T (in kelvin)= 326.15K
P(12)= 10(.0821)(326.15)
If my math is right, you should get around 22.3ATM of pressure. This is a lot, but that makes sense due to the relatively high temperature, and amount of gas compared to STP.