Answer: 4 units.
Step-by-step explanation:
A firm should produce at the rate where Marginal Cost is equal to Marginal Revenue or at a point where they are at their closest.
From the above question, the Marginal Revenue is the Market Price of $60 because that is the extra amount made per sale.
The closest Marginal Cost to $60 is at 4 units. Here the cost of producing is $165 and the cost of producing 3 units is $110. The cost of producing the 4th unit,
= 165 - 110
= $55
The marginal cost of the 5th unit is $80 so it cannot be here.
At the 4th unit the profit made is,
= (Selling price * units) - cost
= (60 * 4) - 165
= $75
This will be the highest profit the company can make.