The volume of nitrogen gas (measured at STP) required to cover a sample of silica gel with a monomolecular layer is $129{\mathrm{cm}}^3/\mathrm{g}\text{ of gel. }$ Calculate the surface area per gram of the gel if each nitrogen molecule occupies $16.2\times {10}^{-20}{\mathrm{m}}^2$ (Report your answer after dividing by 10).