A bag contains 7 green and 8 white balls. If two balls are drawn simultaneously, the probability that both are of the same colour is -.  Choose the correct choice from the following answers.
A) 7 / 18 B) 7 / 19 C) 7 / 11 D) 7 / 12 E) 7 / 15

Rationale: "drawing two balls of same color from seven green balls can be done in ⁷ c ₂ ways . similarly from eight white balls two can be drawn in ways . 7 / 15 answer : e"
Answer: E