In this question, you are given the density (2.7g/ml) and the volume of the aluminum. You are asked how much the volume is. To answer this question, you need to convert the volume into mass. Since the unit used is already same, you don't need to convert it into another unit. The calculation would be:
mass= volume / density
mass= 405ml / (2.70 g/ml)
mass= 150grams
