You owe $25 to a friend. You have paid back $12 but asked for another $8. How much do you owe?

You owe $25 to a friend. You have paid back $12 but asked for another $8. How much do you owe?

You pay back 12, so your balance is:
-25 + 12 = -13 or you owe 13

You ask for (Borrow) another $8
-13 - 8 = -21 or you owe 21