We know that it take 1/6 of a minute to fill up the water bottle up to 1/3 full.
To find how long it will take, we will do:
1/3×3=3/3 This water bottle fraction when it's full
If we do the same thing to the time, we will get:
1/6×3=3/6=1/2
Then we do 1/2×60 to find how long it will take:
1/2×60=60/2=30
So it will take 30 seconds to fill up the water bottle.