I know that because, since at the rate of $2.52 dollars stays the same, you multiply that by the amount half-gallons you need. In this case, we need 4 gallons, so how many half gallons are there in 4 whole gallons? Well, there are 2 halves in one whole, so you multiply 4 and 2 to find out how many half gallons there are. So, in this case it would be 8 half gallons. Now you multiply the amount of half gallons (8) by the standard rate given (2.52) so, 2.52×8=20.16.
