I believe the answer is 16. YES is 3 letters. 1) green all letter 2) green, green, red 3) green, red, green 4) red, green, green 5) red for all 6) red, red, green 7) red, green, red 8) green, red, red. Now "NO" has 2 letters, so he can write any way of "YES" with 2 combinations of "NO"{1) green, red 2) red, green)} so multiply 8 by 2 to get the final answer of 16.