Answer: -3 or -$3.
Explanation:
First, the set of integer numbers is the set of all the whole numbers (negatives, zero, and positives).
We want to write a $3 loss, now, the most important part here is that we have a loss, so we must represent this with a negative number.
Then we can write this as:
"An integer that represents a $3 loss"
is -3 or -$3 (if we want to also respect the units)