Example: I owe Jo $25 and Sam owes me $30. I have $15. If all debts are paid off how much will I have then?
Another example: I live on the same road as my friends Sam, Jo and Alex, who all live further down the road from me. One day I go to visit Jo who lives 25 houses away, then I start walking back home, stopping to visit Alex who lives 15 houses up the road from Jo. If Sam lives 30 houses away from me, how many houses further up the road from Sam does Alex live?