Is z = 5 in the solution set of the inequality 6z > 15

Let m ♣ n be defined as follows: m ♣ n = m^3 - n^3 if x ♣ y = 0, which statement could be true? a) x = 0, y = 1 b) x = 2, y = 2 c) x = -1, y = 0 d) x = -3, y = 3 e) x = 1/2, y = -2