Ideal gas law: PV = nRT
Write down what you know and what you want to fine:
P = pressure = ?
V = volume in liters = 0.950 L
n = moles = 727.2 g x 1 mol CH4 / 16 g = 45.45 moles
R = gas constant = 0.0821 Latm/Kmol
T = temperature in K = 221.9K
Solve for P:
P = nRT/V = (45.45)(0.0821)(221.9) / 0.950
P = 872 atm (3 sig. figs. based on 0.950 L having 3 s.f.)