i got this answer from someone else but it should answer your question
About 6 days
Explanation:
Here the function that shows the population of fish after x weeks,
Where b is any unknown,
If b = 3,
Then, the function is,
Which is a exponentially increasing function,
That having y-intercept = (0,1)
And, horizontal asymptote,
y = 0
End behavior of the function:
As ,
As ,
Thus, by the above information we can graph the given relation.
Now, For at least 100 fish in the pound,
By taking log on both sides,
Thus, after 0.8567 weeks (approx) the fish on the pound will be at least 100.
1 week = 7 days,
0.8567 weeks = 5.9969 days ≈ 6 days
Hence, after 6 days (approx) the fish on the pound will be at least 100.