Every point of that given function is in the form (x,y). The x coordinate is always listed first. The domain is the set of allowed x values of a function. All we do is list the x coordinates of each point. Optionally you sort the x values from smallest to largest just to keep things consistent. Though a set like {1,2,3} is the same as {3,1,2}.
Side note: the range is the set of possible y values of a function
The 4 litres of red has to be 2 parts of the mixture, so each part will be 2 litres. Therefore 3 parts of cream will be 6 litres and the one part of blue will be 2 litres.
