If it triples every month, we would multiply last month's by 3. Sooo...
Month 1: 3 rabbits.
Month 2: 9 rabbits.
Month 3: 27 rabbits.
Month 4: 81 rabbits.
We could keep going, but you're looking for after 3 months, which the answer would be 27 rabbits.
I hope this was helpful! :>