Hello this is my first post , 
I am reading a book called (probability for dummies) the answer in the book for the question below has confused me ...

Suppose you have **four** friends named Jim , Arun , Soma , and Eric. How many ways can you rearrange the individuals in a **row** so that **Soma and Eric** **don't** sit next to each other ?

The answer in the book is 

**18** of the scenarios involved the two **not** sitting next to each other 

I know there are **4!** = **24 ways** to seat the four people 

But I don't understand how the author got to **18** when **2** of them cant sit next to each other 

would really appreciate any help thank you