We know that each generation takes approximately 3 weeks, then, we can estimate how many generations we do have in one year, remember that one year has

Then, in one year we have

In the real world, we can't have half of a generation or a decimal generation, then, let's approximate it to the nearest integer, in that case, 17 generations.
We have the expression that predicts the number of mice, then we can use that equation to find the result for 17 generations:

Evaluate that at x = 17

With an offspring of

And the ending mice

Therefore, the final answer is
