To calculate the molar volume of a gas at STP you can use the ideal gas law equation,
PV=nRT
Regardless of what ideal gas you use, the molar volume at STP will be identical across the board, since you'll be using 1 mole in the ideal gas law equation regardless of what gas you're dealing with.
That is why the volume occupied by 1 mole of any ideal gas will be equal to 22.7 L at STP.
22.4L = 1 mol
38.0L = ?
= 38/22.4
=1.6964285714 Moles