Suppose you have a cookie stand and when you charge $3 per cookie box you sell
250 boxes but when you raise your price to $4 you only sell 120 boxes.
You didn't ask for any solution, so I guess you mean to give an answer to
what you could conclude from that information:
The object is to make the most money, not to sell the most cookie boxes. You
should observe that when you charge $3 you take in 250×$3 = $750 and when
you charge $4 you only take in 120×$4 = $480. So you should conclude that $4
is too much to charge to make the most money. So you should try charging
$3.50. If you still take in less than $750, then try charging $2.50, and
keep on changing the price, every time keeping a record of how much money you
took in, and by trial and error you will eventually find the optimum price to
charge per cookie box so you'll take in the most money possible.
Edwin