A can contains a mixture of two liquids A and B in the ratio 7:5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7:9. How many litres of liquid A was contained by the can initially?
Choose the correct choice from the following options:
A) 25 B) 21 C) 20 D) 10 E) 15
Suppose the can initially contains 7x and 5x litres mixtures A and B   respectively   Quantity of A in mix. left =[7x –7/12 * 9 ] =[7x –21/4]   Quantity of B in mix. left =[5x –5/12 *9 ] = [ 5x - 15/4 ]   Therefore [ 7x-21/4 ] =7/9 or 28x-21 = 7/9   [5x-15/4]+9 20x+21   252x -189  28 -21= 
<gadget id="calculator"> 28 -21</gadget>
<output>7</output>
7/9   [5x-15/4]+9 20x+21   252x -189=140x+147 or 112x =336 , x = 3.   Quantity of A in the can initially =7*3= 
<gadget id="calculator">7*3</gadget>
<output>21</output>
21   ANSWER:21
<result>B</result>
A can contains a mixture of two liquids A and B in the ratio 7:5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7:9. How many litres of liquid A was contained by the can initially?