142. Solving a chemistry problem

After mixing 1,000 g of bone powder with 100 〖cm〗 ^ 3 methylene blue solution with a concentration of 100 μmol / L, the equilibrium concentration of the latter is 60 μmol / L. If you double the weight of coal (2 g), the equilibrium concentration of the solution becomes equal to 40 μmol / L. Calculate the specific surface area of the coal, assuming that the adsorption follows the Langmuir equation. Take the area of the mitylene blue molecule in the monolayer equal to 65 * 〖10〗 ^ (- 20) m ^ 2.