Number of words that can be made using all the letters of the word W, if Os as well as Is are separated is?

I am facing difficulty in solving the 18th Question from the above passage.

Attempt:

I have attempted it using principal of inclusion and exclusion.

Let n be the required number of ways.

$n = \text{Total number of ways - Number of ways in which Os and Is are together}$

$\implies n = \dfrac{12!}{3!2!2!} - \dfrac{11!}{2!3!} - \dfrac{10!}{2!2!}+ \dfrac{9!2!}{2!} = 399 \times 8!$

This gives $N = 399$ which is wrong. Can you please tell me why am I getting the wrong answer?

from Hot Weekly Questions - Mathematics Stack Exchange