Answer :
Looking at it another way, each ml has a mass of 0.7899 g, so how many mls will it take to get 31.8 g?
(x ml)(0.7899 g/ml) = 31.8 g
x = 31.8 g/0.7899 g/ml = 40.3 ml
(x ml)(0.7899 g/ml) = 31.8 g
x = 31.8 g/0.7899 g/ml = 40.3 ml