(i). A firm's costs are 500 when output is 100. If the TC function is linear and fixed cost (FC) are 200, find the marginal cost when Q = 4, 5 and 6.

(ii). The following are estimates of TC and AC function for various firms. Calculate the MC function in each case and say whether, or under what conditions, the MC function is economically meaningful.

(a). AC = 20/Q + 3 + 0.5Q

(b). AC - 2 = 100/Q + 0.2Q² = Q³

(c). TC - 100 - 2Q  + 2Q² = Q³

(d). A.AC = a + bQ - cQ² + gQ³

Where a, b and c are constants.

Given the MC when Q = 4 for (a), (b) and (c).