Rachana borrowed a certain sum at the rate of 15% per annum.

Let the money borrowed by Rachana be Rs $\mathrm{x}$.

Then, we have:

$\mathrm{CI}=\mathrm{P}\left(1+\frac{\mathrm{R}}{100}\right)^{\mathrm{n}}-\mathrm{P}$

$1,290=\mathrm{x}\left[\left(1+\frac{15}{100}\right)^{2}-1\right]$

$1,290=\mathrm{x}[0.3225]$

$\mathrm{x}=\frac{1,290}{0.3225}$

= 4,000

Thus, Rachana borrowed Rs 4,000.