Look first at how revenue relates to price.
price Count Sold Tickets
200 10000
180 11000 ---- here, i=1
160 12000
200-20i 10000+1000i
i is used to count increments of $20.
You may want to express that price .
COST for flying 1 person was given as $100, for ONE PERSON.
KEY IDEA: P=r-c, PROFIT is revenue minus cost, but understand cost will be for all ticket buyers who are to fly.
As your description gives, P is for profit and p is for price of a ticket.
(a) profit in terms of number of tickets sold;
n for count of tickets
---------No way getting away from the unknown ticket price. Otherwise you could simply say .