Example
To produce a quantity Q of lemonade, it costs Zoe $$C \left( Q \right) = 2Q$$ If she makes 2 liters of lemonade, it will cost her $$C \left( 2 \right) = 2 \times 2 = 4$$
Question
Zoe's cost function is $$C \left( Q \right) = 1 Q + 76$$ How much does it cost to produce 6 liters of lemonade?
Plug `Q = 6` into `C \left( Q \right) = 1 Q + 76` \begin{align*} C \left( Q \right) &= 1 Q + 76 \\ &= 1 \times 6 + 76 \\ &= 6 + 76 \\ &= 82 \end{align*}