Romesh took over stock at $\text{Rs. }8,100$, which is $10\%$ less than its book value. The book value of the stock was _________

Let the book value of the stock be $x$.According to the problem statement, Romesh took over the stock at $10\%$ less than its book value:
$$x-10\%\text{ of }x=8,100$$
$$x\left(1-\frac{10}{100}\right)=8,100$$
$$x\left(\frac{90}{100}\right)=8,100$$
$$x=8,100\times \frac{100}{90}$$
$$x=90\times 100=\text{Rs. }9,000$$
So, the book value of the stock was $\text{Rs. }9,000$.