The figures are invented. A firm in a perfectly competitive market sells each unit at the market price of $13. Its total cost per day at outputs 0 to 6 is $8, $15, $21, $29, $39, $51 and $65. (i) State the firm's marginal revenue. [1] (ii) Calculate the marginal cost of the 5th unit and of the 6th unit. [1] (iii) Find the profit-maximising output. [1] (iv) Calculate the profit at that output. [1]

HL Paper 3-style calculation (standalone practice; not an IB question).