It would take 6

hours or 6.25 hours if John uses the 100 watt pump.
There is no common term
Between 2l and l its l
Between 2l and 2 its 2
Between 2 and l there are no common terms, so between 2 l and 2l also there are no common terms
five numbers: 24, 25, 26, 27, 28
the largest is 28
I am attaching a document showing the steps.
Answer:
7:3, 14:6, 28:12
multiples.. hope that helps.