In a box, there are 8 red, 7 blue and 6 green balls. One ball is picked up

In a box, there are 8 red, 7 blue and 6 green balls. One ball is picked up randomly. What is the probability that it is neither red nor green?

Total number of balls = S = (8 + 7 + 6) = 21.
Let E = event that the ball drawn is neither red nor green.
image