The given values in the problem are:
.725 M is moles per liter
300 mL = .300 L
The solution is:
56.1 g/mol in 300 ml = 56.1g/mol in .3L
M = (x gram/56.1) /.3L
.725 = (x gram/56.1)/.3L
Multiply both sides by .3
.2175 = x grams/56.1
x = 12.20 g