The volume of N2 gas of 0ºC and 1.013 bar required to cover a sample of silica gel with uni molecular layer is $129{\mathrm{cm}}^3{\mathrm{g}}^{-1}\text{ of gel. }$ The surface area per gram of the gel if each nitrogen molecule occupies $16.2\times {10}^{-20}{\mathrm{m}}^2\text{ is }\mathrm{x}\times {10}^3$ The value of x = _____