A substance is dissolved in water forming 4.475 M solution

A substance is dissolved in water forming 4.475 M solution. 6.1 L of solution contains 546 g of substance. What is the molar mass of the substance?

1 L contains 4.475 mol so 6.1 L contains 6.1×4.475 = 27.2975 mol = 546 g
∴1 mol = 546/27.2975 = 20.0 g mol^-1 (HF? yikes!)