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 $10 more, the corresponding ratio would have been 5:3. How much was the oil bill for January?	Choose the correct choice from the following choices:
A) $ 60  B) $ 80  C) $ 100  D) $ 120  E) $ 140

Rationale: "3 : 2 = 9 : 6 and 5 : 3 = 10 : 6 . an increase in $ 10 increases the ratio by 1 : 6 . therefore , january ' s bill was 6 ( $ 10 ) = $ 60 . the answer is a ."
Answer: A