Hi, I was looking to get some help with some multiply choice questions! If you could give a small explanation that would be great :)

Given:

=-Q^3+48Q^2-180Q-800 (0Q100)

Which of the following is true?

A.The total profit function is U-shaped because its second derivative is always positive.

B.The total profit function is an inverted-U because its second derivative is always negative.

C.The total profit function has two output levels at which marginal profit is equal to zero.

D.The total profit function is maximized when the monopolist is producing the maximum level of output possible.

E.None of the above is necessarily true.

and...

Which of the following is not true?

A.Marginal revenue is equal to marginal cost when

B.The total fixed cost is zero

C.The output level at which the marginal cost curve cuts the marginal revenue curve from below is

D.The maximum value of the total profit function is

E.Marginal revenue is equal to marginal cost when Which of the following is not true?

thanks