Answer:
$5.25 Dollars
Explanation:
I know that if you divide 21 by 3 you get 7. So, 2/3 of 21 is 14. He spent 14 dollars at the music store. This means that he has 7 dollars left. From here he spend 1/4 of 7 dollars on a drink. 1/4 of 7 is $1.75. This means that he has 5.25 dollars left after he bought the drink! :)
Hope this helped! :)