Task: Question Answering
Input (English): Problem: a can contains a mixture of liquids a and b is the ratio 7: 5. when 18 litres of mixture are drawn off and the can is filled with b, the ratio of a and b becomes 7: 9. how many liter of liquid a was contained by the can initially ?
Options: a. 32, b. 52, c. 62, d. 42, e. 48
Output (English): d