Remember:
Negative plus negative equals negative
Negative plus positive equals positive (under circumsatnces)
Postive minus positive equals positive (when the first number being subracted from second number is a larger number)
You do -16+56 which is 40 and so then 40-63, is -23 (for one week). So then you do 56-63 (for week two), you then get -7. So then you add -23+-7 and get -30 so he has -30£. In other words he is in debt by 30£.
