The question include three parts, however I will just require help with the last part. I just find the first two parts essential for the answer.

The number of applications for a job is 15. Calculate the number of different ways the applicants are selected for interview.(part A)

The six selected applicants are interview in a particular day. (part B) Calculate the ways in which the order of the interviews can be arranged.

Of six applicants interviewthreehave background in business,twobackground in education and one in recreation.

Calculate the number of ways in which the order of the six interviews can be arranged, when applicants have the SAME background are interviewed SUCCESSIVELY. (Part 3 that i dont understand)

I got the answer for part A to be = 15C6=5005

and Part B to be 6!=720

However I was unable to get the answer of part 3, I know from the back of the book that it is 72, but I have no clue why.