Answer:
46 days
Explanation:
Given : Regression equation:

Where,
y = amount of water lilies the pond hold
3.915 = represents the initial population.
1.106 = represents the increase in population at time x.
x = is a variable of time.
The pond can hold 400 water lilies ⇒ y=400
Putting values in equation we get,


Taking log both side
By logarithm property -





Approx. x=46
Therefore, 46th day the pond be full.