In the word ASSASSINATION, we will treat all the vowels that is AAAIIO as one letter only.
Now, we have (AAAIIO)SSSSNNT
This has 8=(7+1) letters of which S occurs 4 times, and N occur 2 times,
Thus, the number of ways of arranging these letters =4!2!8!=840.
Now, 6 vowels in which A occurs 3times, and I occur two times, they can be arranged in 3!2!6!=60 ways.
Therefore, required number of ways=(840×60)=50400.