Calculate the molar m of an unknown metal.?

A student is provided with a sample of alkali metal sulfate, M2SO4, in which the identity of the alkali metal M, is unknown. A m of 0.087 15 g of the compound is dissolved in water and an excess of barium chloride solution is added. This produces a precipitate of barium sulphate, which is filtered off and dried. If the m of the precipitate is 0.1167g, calculate the molar m of alkali metal.