Can someone explain this question?

I’m totally confused and didn’t understand Greg’s explanation for it

Hint:-
image

If you divide the Qty A and Qty B by 3 , you’ll get 5A and 3B respectively.

Given:

multiply the 5(3.0A) and 3 in 3(5.0B)

15.05A > 15.03B —> Eq1

Now , 15.0 is the same in both cases so we only compare
5A to 3B