A sum of money lent out at S.I. amounts to a total of $480 after 2 years and to $680 after a further period of 5 years. What was the initial sum of money that was invested? Choose the correct choice from the following answers.
A) $ 360 B) $ 380 C) $ 400 D) $ 420 E) $ 440

Rationale: "s . i for 5 years = $ 680 - $ 480 = $ 200 the s . i . is $ 40 / year s . i . for 2 years = $ 80 principal = $ 480 - $ 80 = $ 400 the answer is c ."
Answer: C