Please draw the coverage curve

A ranking classifier ranks 25 training examples {xi}, from highest to lowest rank, in the following order: Highest Lowest x2,x3,x1,x5,x13,x6,x8,x7,x9,x10,x12,x11,x15,x4,x14,x21,x17,x20,x18,x22,x16,x19,x25, x23,x24 Examples x1 through x12 are in the positive class (which should be ranked higher); examples x13 through x25 are in the negative class (which should be ranked lower). (a) How many ranking errors are there? (b) What is the ranking error rate? (c) What is the ranking accuracy? (d) Draw the coverage curve for the ranking classifier on this dataset