Murphy Cord Company produces replacement adapter power charger cords that it sells for $$20$ each. Each power charger cord costs $$6$ of variable costs to make. During April, $700$ power charger cords were sold. Fixed costs for April were $$4$ per unit for a total of $$2,800$ for the month. How much will Murphy's operating income increase for each $$1,000$ increase in monthly revenue?

Question $11$ options:

$1)$

$$700$

$2)$

$$500$

$3)$

$$600$

$4)$

Not enough information to determine the answer.