How do you solve this problem and get the answer?

Question

A glass jar contains 4 red marbles, 6 blue marbles, and 5 green marbles. The probability that Alexa would select a blue marble is 6/15. Which is the probability that Ryan would select a marble that is not blue?

Answer 1

1- Pr(B) = Pr(not B) = 1 - 6/15 = 15/15 - 6/15 = (15-6)/15 = 9/15

or

(4+5)/(4+6+5) = 9/15 = Pr(picking one that is not blue)