Given a monopolist with a maximum output of Q = 180 (Q is measured in tones of iron per day and can only take negative values). The monopolist's demand curve looks like

Q= 200 - 1/2 * P (* = times)

where "P" denotes the price of iron ore measured in dollars per tone, and the total cost of producing iron ore is described by the function:

TC= 0.2 * Q^2 + 4 * Q + 400

The marginal cost curve cuts the marginal revenue curve when the output level is what?