He has a change of $0.24 after paying for items with a $10 bill
If take note of what he bought, he bought 1 ruler ($0.79), three pens ($4.47), and two notebooks ($4.50). So when you add them up, you get a total of $9.76 for all of the items, and since he payed with a ten dollar bill, we subtract 10 by the total ($9.76) and you get 0.24.