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 $30 more, the corresponding ratio would have been 5:3. How much was the oil bill for January?
Select.
A) $ 120	B) $ 150	C) $ 180	D) $ 210	E) $ 240

Rationale: "3 : 2 = 9 : 6 and 5 : 3 = 10 : 6 . an increase in $ 30 increases the ratio by 1 : 6 . therefore , january ' s bill was 6 ( $ 30 ) = $ 180 . the answer is c ."
Answer: C