What's a real world situation for 7.50y + 9

The super market is having a sale of 1 bag of chips for $7.50

Y = bag of chips

you can buy a liter of soda for an extra $9

if I buy 3 bags of chips and one liter of soda how much will my total be before tax?

22.59

(7.50 x 3) + 9 = 22.59