18. For a foxced cost, as volume increases: a. the cost behaviour depends on the type of fixed cost involved b. total fixed costs remain constant and fixed costs per unit increase c. both total fixed costs and fixed costs per unit remain constant d. total fixed costs remain constant and fixed costs per unit decrease 19. Antonio plc takes 60 days to pay for goods purchased from its main supplier. To encourage more prompt payment the supplier has offered the company a 3 per cent discount if payment is made within 10 days. However, Antonio pic has refused to accept the offer. What is the approximate annual cost of the discount foregone? a. 21.9% I b.18.2% 18.0% d. 0.4% c