9.15 For each of the following independent situations, calculate the break-even point in units. a. Variable cost per unit of $2, annual fixed costs of $60 000 and selling price per unit of $6. b. Variable costs per unit of $10, annual fixed costs of $120 000 and selling price per unit of $20. c. Variable costs per unit of $15, annual fixed costs of $90 000 and selling price of $18