Surface area of synthetic zeolite 13x by gas adsorption

The adsorption of argon gas has been measured on synthetic zeolite 13x at 77.3K and Vm the monolayer coverages has been obtained by the "point B" method from the monolayer adsorption isotherm. The standard surface area of argon gas is known to be 11.5 Å2. Using these two properties, the specific surface area ? of the synthetic zeolite 13x has been calculated as 460 m2/g.