There is a total of 90 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/3 and the probability that it will be green is 1/5. What is the probability that the marble will be either red or blue?
Choose the most appropriate option.
A) 1 / 3
B) 3 / 5
C) 7 / 15
D) 11 / 30
E) 17 / 30

Rationale: "p ( red or blue ) = 1 - p ( white ) - p ( green ) = 15 / 15 - 5 / 15 - 3 / 15 = 7 / 15 the answer is c ."
Answer: C