Use the distributive property and expand 28, then distribute the 4 to 20 and the 4 to 8. Then you have 18 + 80 + 32. Use commutative property to reverse the order of 32 and 80 so that 18 and 32 are friendly numbers to add.
If you know the whole price for 2.4 gallons, divide the whole price by 2.4 to get the cost for one, because when you multiply the cost for 1 by 2.4, you get the total.
