Example
The demand for cookies follows the equation: `Q_d = 10 - P`.
If price is $3, the quantity demanded is `Q_d = 10 - 3 = 7` cookies.
Question
The demand for cookies follows the equation: `Q_d = 653 - 45 \times P`.
If cookies were sold on the market for $14, what is the quantity demanded?
Plug the price $14 into the demand function: $$Q_d = 653 - 45 \times P = 653 - 45 \times 14 = 23$$