Start with 2 rabbits, each pair has 4 babies per month.

After 12 months, you will have 12,288 bunnies.

Showing my work:

1st month, 6 bunnies
2nd month, 12 bunnies
3rd month, 24 bunnies
4th month, 48 bunnies
5th month, 96 bunnies
6th month, 192 bunnies
7th month, 384 bunnies
8th month, 768 bunnies
9th month, 1,536 bunnies
10th month, 3,072 bunnies
11th month, 6,144 bunnies
12 month, 12,288 bunnies

128/3reason being 5 and 1/3 = 16/316/3 • 2/3 = 32/31 and 1/3 = 4/3 32/3 • 4/3 this will equal 128/3