The situation that describes opposite quantities that when combined would equal 0 is:
A deposit of $20 to a bank and a fee charged of $20.
In this scenario, the deposit of $20 and the fee of $20 are opposites: the deposit is a positive quantity (+$20), and the fee is a negative quantity (-$20). When combined, they equal 0:
\(+20 + (-20) = 0\)
This means that the net effect is neutral, resulting in no change in the balance.