Let N be a positive multiple of 5 . One red ball and N green balls are arranged in a line in random order. Let P(N) be the probability that at least \dfrac{3}{5} of the green balls are on the same side of the red ball. Observe that P(5)=1 and that P(N) approaches \dfrac{4}{5} as N grows large. What is the sum of the digits of the least value of N such that P(N)<\dfrac{321}{400} ?

**Answer Choices**

A. 12

B. 14

C. 16

D. 18

E. 20