If 75% of the students in a middle school ride the bus home, and that is 225 students,

The original price was $50.

To find this we need to start with the price you paid ($28). We then use this cost to find the pre-coupon price. Since the coupon affords a 20% discount, that means you pay for 80%. To solve this, simply divide the price you paid by the percentage you paid.

$28/.80 = $35.

Now that we have the pre-coupon price ($35), we can use that to find the original price. Again, we'd want to divide that by the percentage you paid for, which is 70%.

$35/.70 = $50