What mass of CH4 would take up 30 L at STP

Please help. Can you guys explain to me the approach and the formula you use for it.

What mass of CH4 would take up 30 L at STP?
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30 liters/22.4 liters/mole at stp = 1.34 moles of CH4.

12 grams/mole x 1.34 moles = 16.1 grams