To find how many moles of the gas you can use ideal gas formula. Remember to change the temperature unit to Kelvin. Since the pressure using kpa, the constant used would be 8.314 kpa*L / mol*K
PV=nRT
n= PV/RT
n= 17,250 kpa * 20 / 8.314 * (24+273.15)K
n=139.64moles