The boiler of a refrigerator is designed to operate at T = 15°F. Assuming Freon® 22 in the liquid and vapor phases can be described by the van der Waals equation with the parameters a = 40,100 psia-ft⁶/lb-mol² and b = 1.60 ft³/lb mol, compute the vapor pressure of Freon^® 22 at T = 15°F.