I think you are trying to find the unit rate.
It was 16 dollars for 3 gallons.
16:3
Divide both sides by 3.
5.333 repeating was how much one gallon was. Or, 5 and 1/3.
If each gallon is 16,
16*3= 48
48 was the total amount.
I dont know what you’re asking for, so I gave you two answers. I hope one fits your needs.
~kaikers