What mass of CH4 is contained in a 581 mL sample of CH4 at −42◦C and 292 torr?

For CH₄ :
Pressure, P = 292/760 atm
Volume, V = 581 mL = 0.581 L
Temperature, T = (273 - 42) K = 231 K
Gas constant, R = 0.0821 atm L / (mol K)
Molar mass, M = (12.01 + 1.008×4) = 16.04 g/mol

PV = nRT
PV = (m/M)RT
m = PVM/(RT)

Mass of CH₄
= (292/760) × 0.581 × 16.04 / (0.0821 × 231) g
= 0.189 g