The total cost function for x units of a commodity is given by:

$C(x)=4 x^3+\frac{x^2}{5}+6 x-5$

The marginal cost when 5 units are produced is:

308

The correct answer is Option (3) → 308

$C(x) = 4x^3 + \frac{x^2}{5} + 6x - 5$

$\text{Marginal cost} = C'(x)$

$C'(x) = 12x^2 + \frac{2x}{5} + 6$

$C'(5) = 12(25) + \frac{2(5)}{5} + 6$

$= 300 + 2 + 6 = 308$

$\text{Marginal cost at } x=5 \text{ is } 308$