For each store what is the ratio of the numbers of cans to the price

2/24 = 9/n 2 times 4.5=9, so 24 times 4.5=108. n=108, so the the answer is 9/108 for Shop Smart.

4/12 = 9/a 4 times 2.5=10, so 12 times 2.5 = 30. a = 30, so the answer is 10/30 for Super Saver.

3/12 = 9/b 3 times 3 = 9, so 12 times 3 = 36. b = 36, so the answer is 9/36 for Price Buster.