If a 1.0L flask is filled with 450 torr of SiH4 gas at 20 °C, what is the mass of SiH4 in the flask?

For the SiH₄ gas :
Pressure, P = 450/760 atm
Volume, V = 1.0 L
Gas constant, R = 0.0821 atm L / (mol K)
Temperature, T = (273 + 20) K = 293 K
Molar mass, M = (28.1 + 1.0×4) g/mol = 32.1 g/mol

PV = nRT and n = m/M
Then, PV = (m/M)RT
m = PVM/(RT)

Mass, m = (450/760) × 1.0 × 32.1 / (0.0821 × 293) g = 0.790 g