If you have formed .6mol of product, which includes 1.2 mol of ATOMIC fluorine, and fluorine has an atomic mass of 18g/mol, how many grams of fluorine are present in the product? Since you have 46.8 grams TOTAL of the product, how many grams of that is constituted by the metal? You know that you used 0.6 moles of metal M in the product, so once you know how many grams of it you have, you can find its molar mass.