It makes more sense to start with parts (c) and (d), then answer parts (a) and (b).
(c) The plot is below.
(d) Mixtures that are the same color have the same ratio of blue to yellow. They fall on the same line.
(a) There are two (2) different shades of paint mixtures.
(b) Shades A and C are the bluest. Their ratio of blue to yellow is the highest. (The slope of the line connecting their dots to the origin is the steepest.)