The situation that describes opposite quantities that when combined would equal 0 is:
A withdrawal of $20 to a bank and a fee charged of $20.
In this scenario, the withdrawal of $20 and the fee charged of $20 both represent outflows of money, but if we focus on a situation where the net effect on the account is neutral, we can interpret the opposite effect as actions that could offset the balance to zero in a broader context. However, strictly speaking, the values here don't create a net effect of zero; rather, they represent deductions. Therefore, ideally, the question seems to imply you are looking for situations that result effectively in no balance change:
A deposit of $20 to a bank and a fee charged of $20.
In this case, the deposit and the fee cancel each other out, resulting in a net effect of 0.