Example
The price for lemonade $$P = 10 - 2 Q$$ Zoe is the only lemonade seller on her street. She controls the quantity of lemonade available on the market.
Her revenue is $$R \left( Q \right) = PQ = \left( 10 - 2Q \right) Q = 10 Q - 2 Q^2$$ If Zoe produces Q=2 liters of lemonade, her revenue is equal to $12: $$R \left( 2 \right) = 10 \times 2 - 2 \times 2^2 = 20 - 8 = 12$$
Question
The price for lemonade follows $$P = 86 - 7 Q$$ What is Zoe's revenue function? What is her revenue if she produces 4 liters of lemonade?
Zoe's revenue function is \begin{align*} R \left( Q \right) &= P Q \\ &= \left( 86 - 7 Q \right) Q \\ &= 86 Q -7 Q^2 \end{align*}
If `Q=4`, then her revenue is \begin{align*} R \left( 4 \right) &= 86 \times 4 - 7 \times 4^2 \\ &= 344 - 112 \\ &= 232 \end{align*}