Answer:
Unfortunately, they charged a high-interest rate on the loan.
The past tense of the verb “charge” is "charged".
Step-by-step explanation:
When the action is done in the past, the verb used to denote the action is known as past tense. In order to change a verb in past tense '-ed' is added to the verb. It shows the action has been done and is completed. In the above sentence, the verb "charged" shows that the action of charging has been done in the past. In the present, it has nothing to do.