Two's complement, two parallel lines intersect at the point (1,1) (2,2) (3,3) .......... u = min (coffee, tea).
3 Perfect substitute for coffee 1 tea 2, together. Take 2 for coffee, 4 for tea, and so on. U= coffee+tea /2.
4 disgust, no proportion is given, assuming that a cup of tea cancels a cup of coffee, the straight line Y=X moves to (1 tea, 0 coffee).