XYZ Inc. sells a single product for $$10$ per unit. Variable production costs are $$5$ per unit. Fixed overhead costs amount $$10,000$ per month. Variable selling costs are $$1$ per unit. Fixed selling costs are $$5,000$ per month. Last month, the company produced $10,000$ units and sold $8,000$ units. If sales were to increase by $4,000$ units, by how much would operating profit increase?

a$.$

$$8,000$

b$.$

$$10,000$

c$.$

$$16,000$

d$.$

$$4,000$