The 3 is distributed to the a+b inside the brackets........
Each friend will have 4 cookies.
The domain is all of the x values in a set and the range is all of the y-values in a set.
If you have a bunch of points such as (3,6), (7,2), (1,5) the domain would be stated as D={3, 7, 1} and the range would be stated as R={6,2,5} If you have a line, then the domain and range would be set up differently. For example, if you have a line with end points at (-3,2) and (5,8) then the domain would be D=(-3,5) and the range would be R=(2,8)
To fill:
6 hours = 1 tank
1 hour = 1/6 tank
To drain:
It takes 4 times as long, therefore 4 x 6 = 24
24 hours = 1 tank
1hour = 1/24 tank
If both pipes are open
1 hour = 1/6 - 1/24 = 1/8 tank
1/8 tank = 1 hour
8/8 tank = 1 x 8 hour
1full tank = 8 hours