Yes you have a good example.
x = number of cookies
2*x = total amount spent on cookies at $2 each
2x-3 = amount you pay after the $3 discount is applied one time for the entire order
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a more numeric example may be this
Lets say you bought 12 cookies, so x = 12
This means it costs 2*x = 2*12 = 24 dollars total if the discount doesnt apply
However, the 3 dollar discount is there, so the grand total is 24-3 = 21 dollars.
