Martha Manufacturing produces a single product that sells for $80. Variable costs per unit equal $32. The company expects total fixed costs to be $72,000 for the next month at the projected sales level of 2,000 units. Suppose management believes that a $24,000 increase in the monthly advertising expense will result in a considerable increase in sales. Sales must increase by how much to justify this additional expenditure?

a. 200 units. b. 334 units. c. 500 units. d. 700 units.