So first you need to multiply 3 and 1.97 which equals 5.91 and that is for Matthew. Now for Jose, you multiply 3 by 3.99 and that equals 11.97. And so to find out how much money they each spend you subtract 11.97 and 5.91 which is 6.06. And to find out how much each gallon of milk is you divide 6.06 by two which is 3.03. So then you multiply 3.03 by 4 because Matthew purchased 4 gallons of milk and that is equal to 12.12 then you multiply 3.03 by 2 for Jose's milk and that equals 6.06. Matthew's total is 5.91 plus 12.12 and that is 18.03. Jose's total is 11.97 plus 6.06 and that equals 18.03 also. Both Matthew and Jose spent $18.03 on groceries and each gallon of milk costs $3.03.