Hey there! From the given compounds and the weights, you can easily identify the limiting reactant to be K2 PtCl4 since you have a 1:2 ratio for NH3 and the molar mass of K2 PtCl4 is 415.09 g/mol meaning you can’t even make half a mole of K2 PtC4 with 54.6g which makes it obvious that it is the limiting reactant. You can compute it using the normal way but I'll skip that for this solution to not make it any longer than it is already. I've posted the step by step solution below. I hope this helps!