Discount comics is running a special: 20 comics for $5.00. seth purchases 30 comics for $7.50. what is the sale price per comic

The difference between 10 comics is $2.50. So $2.50 / 10 = .25 (25 cents?) for one comic.
To check if this is correct you can do 20 x .25 which equals $5.
Each comic costs 25 cents. (Sorry if it isn't cents I don't use this currency.)