Question:
The total revenue received from the sale of $x$ units of a product is given by $R(x)=13 x^{2}+26 x+15$. Find the marginal revenue when $x=7$.
Solution:
Since the marginal revenue is the rate of change of total revenue with respect to its output,
Marginal Revenue $(\mathrm{MR})=\frac{d R}{d x}(x)=\frac{d}{d x}\left(13 x^{2}+26 x+15\right)=26 x+26$
When $x=7$
Marginal Revenue $(\mathrm{MR})=26(7)+26=182+26=$ Rs 208