Answer: Option A
$$\eqalign{
& {\text{10}}\% {\text{ = }}\frac{1}{{10}} \cr
& {\text{Principal}}\,\,\,\,\,\,\,{\text{Amount}} \cr
& \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr
& \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr
& \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr
& \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr
& \underbrace {\overline {\,\,\,10000\,\,\,\,\,\,{\text{:}}\,\,\,\,\,{\text{14641}}\,\,\,} }_{{\text{CI = 4641}}} \cr
& \because {\text{Principal = 10000 units}} \cr
& {\text{ = Rs}}{\text{. 4000 (given)}} \cr
& {\text{1 unit = }}\frac{2}{5} \cr
& {\text{CI = 4641 unit}} \cr
& {\text{ = Rs}}{\text{. }}\left( {\frac{2}{5} \times 4641} \right) \cr
& = {\text{Rs}}{\text{. }}1856.40 \cr} $$