(d) 5%
P = Rs 8000, C.I. = Rs 1261
\(\Rightarrow\) Amount = Rs 9261, n = 3, r = ?
\(\therefore\) 9261 = 8000\(\big(1+\frac{r}{100}\big)^3\)
\(\Rightarrow\) \(\big(1+\frac{r}{100}\big)^3\) = \(\frac{9261}{8000}\) = \(\big(\frac{21}{20}\big)^3\)
\(\Rightarrow\) 1 + \(\frac{r}{100}\) = \(\frac{21}{20}\)
\(\Rightarrow\) \(\frac{r}{100}\) = \(\frac{21}{20}\) - 1 =\(\frac{1}{20}\)
\(\Rightarrow\) r = \(\frac{100}{20}\)% = 5% p.a.