In what time will Rs. 1860 amount to 2641.20 at simple interest 12% per annum ?

$$\eqalign{ & {\text{Rate }}\% = {\text{12}}\% \cr & {\text{Principal = Rs}}{\text{. 1860}} \cr & {\text{Amount = Rs}}{\text{. 2641}}{\text{.20}} \cr & {\text{Interest}} \cr & {\text{ = Rs}}{\text{. }}\left( {2641.20 - 1860} \right) \cr & = {\text{Rs}}{\text{. 781}}{\text{.20}} \cr & {\text{By using formula,}} \cr & {\text{Required time }} \cr & = \frac{{781.20 \times 100}}{{1860 \times 12}} \cr & = 3\frac{1}{2}{\text{ years}} \cr} $$