Company A sells its product for $2.50 per unit and generates a 30% contribution margin percentage. The company's fixed costs are $6,500 per month. Company A is currently selling 15,000 units per month. If the company wants to increase operating income by 20%, how many additional units must be sold? (round to the nearest whole number.)

a 5,666

b 1,267

c 1,333

d 1,166