A certain sum is invested at simple interest at 15% p.a. for two years instead of investing at 10% p.a. for the same time period. Therefore the interest received is more by Rs. 840. Find the sum?	Choose the correct choice from the following options:
A) s . 8400	B) s . 9000	C) s . 14000	D) s . 17000	E) s . 27000

Rationale: "let the sum be rs . x . ( x * 15 * 2 ) / 100 - ( x * 10 * 2 ) / 100 = 840 = > 30 x / 100 - 20 x / 100 = 840 = > 10 x / 100 = 840 = > x = 8400 . answer : a"
Answer: A