The formula for ideal gas law is:
P V = n R T
where
P is pressure = ?
V is volume = 1.50 L
n is number of moles = 1.57 mol
R is gas constant = 0.08205746 L atm / mol K
T is temperature = 273 K
P = 1.57 mol * 0.08205746 L atm / mol K * 273 K / 1.50 L
P = 23.45 atm