Question 1054799
Look first at how revenue relates to price.
<pre>
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.
</pre>


You may want to express that price {{{p=200-20i}}}.


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;
{{{P=r-c}}}
n for count of tickets
{{{P=r-c*n}}}
{{{highlight(P=(200-20i)n-100n)}}}---------No way getting away from the unknown ticket price.  Otherwise you could simply say  {{{highlight(P=pn-100n)}}}.