Two friends, alejandro and mia, agreed to split the check at a restaurant. alejandro ordered $\$12$ worth of food and mia ordered $\$18$ worth. at the end of the meal, alejandro put his $\$12$ contribution on the table, plus a $20\%$ tip on his bill and mia put her $\$18$ contribution on the table, plus a $15\%$ tip on her bill.

the total tip left by alejandro and mia is equal to $r\%$ of the total check for their table, where the "total check" amount does not include the tip. what is $r$?