One serving of whole milk contains 8 grams of fat. reduced-fat milk contains 41.25% less fat per serving than whole milk. how many grams of fat does one serving of reduced-fat milk contain?

We are told the reduced fat milk has 41.25% less fat than whole milk.

So the reduced fat milk has 58.75% of the fat of whole milk (that is, 100% -41.25%).
A serving of whole milk has 8 grams of fat.
So a serving of reduced fat milk has .5875 * 8 g = 4.7 g of fat.

The density of the cube is 40