The total heat released, Q, equals number of moles, n, times molar heat of fussion, Hf. this is: Q = n * Hf. You kno Q and Hf, so you can find n as n = Q/Hf = 235.0 kJ / 12.55 kJ/mol = 18.72 mol. Now you can pass that to mass using the atomic mass of Au, which is 197 g/mol => mass = 18.73 mol * 197 g/mol = 3688.9 grams.
