The money to be spent for the welfare of the employees of a firm is proportional to the rate of change of its total revenue. If the total revenue (in ₹) received from the sale of $x$ units of a product is given by $R(x) = 3x^2 + 36x + 5$, find the marginal revenue, when $x = 5$.

₹66

The correct answer is Option (2) → ₹66 ##

Total revenue is given by $R(x) = 3x^2 + 36x + 5$

Marginal revenue $\frac{dR}{dx} = 6x + 36$

At $x = 5$, $\left( \frac{dR}{dx} \right)_{x=5} = 6 \times 5 + 36 = ₹66$