The ratio of the amount of the oil bill for the month of February to the amount of the oil bill for the month of January was 3:2. If the oil bill for February had been $20 more, the corresponding ratio would have been 5:3. How much was the oil bill for January?
Choose the correct choice from the following
A) $ 100  B) $ 120  C) $ 140  D) $ 160  E) $ 180

Rationale: "3 : 2 = 9 : 6 and 5 : 3 = 10 : 6 . an increase in $ 20 increases the ratio by 1 : 6 . therefore , january ' s bill was 6 ( $ 20 ) = $ 120 . the answer is b ."
Answer: B