Suppose that a firm in a competitive market faces the following revenues and costs: QuantityTotal RevenueTotal Cost 0$0$3 1$7$5 2$14$9 3$21$15 4$28$23 5$35$33 6$42$45 7$49$59 Refer to Table 14-10. This firm should continue to produce and sell units as long as the marginal cost of production is less than or equal to 1.a$3. b$7. c.$9. d$5.