Question

66.9 g of a substance X dissolves in enough water to make 0.428 L of a 0.68 M solution. Calculate the molar mass of X in g/mol.

Answer 1

mL x M x millimolar mass = grams
OR
mols = M x L = ?
Then mol = grams/molar mass. You know grams and mols, solve for molar mass.