In this task, you need to provide the correct option for a given problem from the provided options.

[EX Q]: Problem: 200 liters of a mixture contains milk and water in the ratio 4 : 1 . if 20 liters of this mixture be replaced by 20 liters of milk , the ratio of milk to water in the new mixture would be ? 
Options: a ) 6 : 1 , b ) 1 : 6 , c ) 2 : 3 , d ) 3 : 2 , e ) 4 : 1
[EX A]: a

[EX Q]: Problem: in assembling a bluetooth device , a factory uses one of two kinds of modules . one module costs $ 15 and the other one , that is cheaper , costs $ 10 . the factory holds a $ 140 worth stock of 13 modules . how many of the modules in the stock are of the cheaper kind ? 
Options: a ) 20 , b ) 25 , c ) 30 , d ) 11 , e ) 35
[EX A]: d

[EX Q]: Problem: what is the square root of 6,561 ? 
Options: a ) 18 , b ) 9 , c ) 45 , d ) 62 , e ) 81
[EX A]:
e