Hi, I was going through PrepSwift content and in the Restrictive permutation video, there is a question that is solved using counting method with restriction (Screenshot of question and solution in given below)

I agree with the method and the solution.

- But how can I get the same answer using the concept of

Restriction = no restriction (total) - restriction is not followed

If I am correct, total number of ways to arrange these books without restriction will be 7 * 6* 5* 4 = 840

How, can I get number of ways where restriction is not followed.

Thanks for the help in advance