AUTO ANSWER (AFTER SEVERAL DAYS):

The least common multiple (LCM) of 12 and 20 is 60. So let the number of 12-ounce cans of soda that Dewey buys be 5, and let the number of 20-ounce bottles of soda that Peppar buys be 3. They each get a total of 60 ounces, but Dewey spends 5 × 1.00 = $5.00, and Peppar spends 3 ×1.25 = $3.75. Peppar spends 5.00 – 3.75 = $1.25 less than Dewey, which is 1.25 ÷ 5.00 × 100 = 25, so P = 25.