A bucket contains 2 mixtures A and B in the ratio 7:5. If 9 liters of the mixture is replaced by 9 liters of liquid B, then the ratio of the two liquids becomes 7:9. How much of the liquid A was there in the bucket?	Choose the correct choice from the following answers:
A) 15liters B) 21liters C) 12liters D) 18liters E) 25liters
1st ratio = 7:5   2nd ratio = 7:9   Difference of cross products ratio = 7*9-7*5= 
<gadget id="calculator">7*9-7*5</gadget>
<output>28</output>
28   common factor of the 1st ratio= (quantity replaced/sum of terms in 1st ratio) + (Quantity replaced*term A in 2nd ratio/Difference)   = (9/7+5) + (9*7/28) = 3   Quantity of A = 7*3= 
<gadget id="calculator">7*3</gadget>
<output>21</output>
21liters   Answer is 21liters
<result>B</result>
A bucket contains 2 mixtures A and B in the ratio 7:5. If 9 liters of the mixture is replaced by 9 liters of liquid B, then the ratio of the two liquids becomes 7:9. How much of the liquid A was there in the bucket?