A certain sum amounts to Rs. 4280 after 14 years and to Rs. 9630 in 16 years when invested at (2R – 10) % per annum compound interest. Find the difference between simple interest earned on Rs. 3250 for 4 years at (R – 6) % per annum and compound interest on the same sum for 2 years at ​ [(R/2) + 5 %] per annum?