A #37.5*g# mass of #"aluminum sulfate"# was obtained from the reaction between #AlBr_3# and #"potassium sulfate"#. What were the starting masses of the reactants?
We follow the stoichiometric equation (which you have represented):
Molar quantities are as follows:
Given the stoichiometry, initially there were
Note that the question is a bit naive and does not reflect chemical reality. As I recall, aluminum sulfate has some solubility in aqueous solution, and the assumption that it would all precipitate is incorrect.