Given that Justin gave the clerk $20 to pay a bill of $6.57.
Now we have to find how much change should justin get.
Justin will recieve change only if he paid more money that the bill amount.
Clearly $20 (paid money) is more than $6.57 (bill amount)
Hence Justin will recieve difference of both values.
To find the difference, we subtract 6.57 from 20
20-6.57= 13.43
Hence Justin will get change of $13.43
