A firm currently produces 2,500 units of output per week. After an additional worker is hired, output rises to 2,620 units per week. If the weekly wage paid to a worker is $480, what is the firm's short-run marginal cost? (Hint: MC is always change in Total Cost/change in output)

a)

$4

b)

$480

c)

None of the answers are correct.

d)

$120