If the average cost function of producing and marketing x units of an item is $AC=2 x-11+\frac{50}{x}$, then the marginal cost function is:

$2 x^2-11 x+50$ $2-\frac{50}{x^2}$ $4 x-11$ $4 x+39$

$4 x-11$

The correct answer is Option (3) → $4 x-11$