Solution: 
                      		$$\eqalign{
  & BD\,{\text{for}}\,3\,{\text{years}} = {\text{Rs}}{\text{.}}\,1116  \cr 
  & BD\,{\text{for}}\,4\,{\text{years}} = \frac{{1116}}{3} \times 4  \cr 
  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{. }}1488  \cr 
  & TD\,{\text{for}}\,4\,{\text{years}} = {\text{Rs}}{\text{.}}\,1200  \cr 
  & F = \frac{{BD \times TD}}{{BD - TD}}  \cr 
  & \,\,\,\,\,\,\, = \frac{{1488 \times 1200}}{{1488 - 1200}}  \cr 
  & \,\,\,\,\,\,\, = \frac{{1488 \times 1200}}{{288}}  \cr 
  & \,\,\,\,\,\,\, = \frac{{124 \times 1200}}{{24}}  \cr 
  & \,\,\,\,\,\,\, = \frac{{124 \times 100}}{2}  \cr 
  & \,\,\,\,\,\,\, = 62 \times 100  \cr 
  & \,\,\,\,\,\,\, = {\text{Rs}}{\text{.}}\,6200 \cr} $$
⇒ Rs. 1488 is the simple interest on Rs. 6200 for 4 years
$$\eqalign{
  &  \Rightarrow 1488 = \frac{{6200 \times 4 \times R}}{{100}}  \cr 
  &  \Rightarrow R = \frac{{1488 \times 100}}{{6200 \times 4}}  \cr 
  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{372 \times 100}}{{6200}}  \cr 
  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{372}}{{62}}  \cr 
  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 6\%  \cr} $$