Brenda's mother made cookies for 11 guests but 10 guests did not come. If she prepared 15 cookies and each guest had the same number of cookies How many did each of them have?
There were 11 guests in total. 
10 of those guests did not come. 
That means that 1 guest did come. 
If she prepared 15 cookies and each guest had the same number of cookies, that means that the 1 guest who came would have had 15 cookies. 

Therefore, each guest would have had 15 cookies.