Answer:
The first 4 guests can arrive at party in 1365 ways if 15 guest have been invited
Explanation:
Total number of guests invited = 15
We are supposed to find in how many ways can the first 4 guest arrive at a party if 15 guest have been invited
We will use combination
Formula :

Substitute n = 15 and r = 4
So,Total no. of ways =

Hence the first 4 guests can arrive at party in 1365 ways if 15 guest have been invited