A firm produces and sells goods in a perfectly competitive market.

The firm's cost depends on the quantity produced.

The total cost function is: C(Q)= 2Q^3 - 20Q^2 + 200Q +392

The firm will produce a positive (>0) quantity if the market price is at least equal to its shut-down price.

What is this firm's shut-down price?

1) Shut-down price less than $100

2) Shut-down price at least $140 but less than $160

3) Shut-down price at least $100 but less than $120

4) Shut-down price at least $120 but less than $140

5) Shut-down price at least $160 ($160 or more)