Question 702662
Drawing a picture for this is difficult but not so bad on paper.


How much bigger is the volume of the second pool than the first pool?  Really, how many times bigger is it?


Using w=width, d=depth, L=length,
{{{V[1]=w*d*L}}}
{{{V[2]=2w*d*4L}}}, and then {{{V[2]=8*w*d*L}}}


There you see that the second pool is 8 times more volume than the first pool.
Since the pipe needs 2 days to fill first pool, we now know 16 days to fill the second pool.