Answer: The profit at the optimal quantity will be $16.
Explanation: The producer will choose a quantity where,
MC≤MR
This happens at the 4th unit of output. So 4 units will be the optimal quantity.
[tex] Profit= TB -TC
=$64 - $48
=$16 [/tex]
After the 4th unit profit starts falling. So, the producer will never choose to produce the 5th unit.