A sum was put at simple interest at a certain rate for 6 years Had it been put at 4% higher rate, it would have fetched 144 more. Find the sum.  Choose the correct choice:
A) 500	B) 600	C) 700	D) 800	E) 900

Rationale: "difference in s . i . = p × t / 100 ( r 1 − r 2 ) ⇒ 144 = p × 6 x 4 / 100 ( ∵ r 1 - r 2 = 2 ) ⇒ p = 144 × 100 / 6 × 4 = 600 answer b"
Answer: B