A sum of money at a simple rate of interest `i_1` , doubles in 5 years. At another simple rate of interest `i_2` , it becomes three times in 12 years. Then, the two rates of interest `i_1` and `i_2` respectively are `10 %` , `16 2/3%` (b) `10 % ,\ 20 %` (c) `20 % ,\ 16 2/3%` (d) `20 % ,\ 30 %`