A firm's research department has estimated that if other firms in the industry are indifferent to change in the price of its product, its demand curve will be:

Qd = 3000 - 200p

However if other firms always charge the same price it does, the firm's demand curve will be

Q_M = 1500 - 50p

Illustrate that MC = 15 is price rigid. All curve must be labelled.