Company currently produces and sells 4,000 units of a product that has a contribution margin of $5 per unit. The company sells the product for a sales price of $20 per unit. Fixed costs are $20,000. The company has recently invested in new technology and expects the variable cost per unit to fall to $12 per unit. The investment is expected to increase fixed costs by $15,000. After the new investment was made, how many units had to be sold to break-even? (Do not round intermediate calculations.)