24: 4.5-0.55 * 3 = 4.5-1.65 = 2.85 0.55 * 3 =1.65, which is below the warning line.

25: 80-40 = 40, 50-30 = 20, then the more stores delivered to No.1 Middle School, the better. Store transportation to 1 middle school.

Then 40x+(8-x) * 30+(6-x) * 80+(1 0-(6-x)) * 50 = 840x = 4, so the best three methods are to transport 6 sets to1.