In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[Q]: Problem: a water tank is four - fifths full . pipe a can fill a tank in 10 minutes and pipe b can empty it in 6 minutes . if both the pipes are open , how many minutes will it take to empty or fill the tank completely ? 
Options: a ) 6 , b ) 9 , c ) 10 , d ) 12 , e ) 15
[A]: d


[Q]: Problem: if two girls starting from same point , walking in the opposite directions with 7 km / hr and 3 km / hr as average speeds respectively . then the distance between them after 12 hours is ? 
Options: a ) 120 , b ) 121 , c ) 122 , d ) 123 , e ) 124
[A]: a


[Q]: Problem: two spherical balls lie on the ground touching . if one of the balls has a radius of 4 cm , and the point of contact is 6 cm above the ground , what is the radius of the other ball ? 
Options: a ) 10 cm , b ) 12 cm , c ) 14 cm , d ) 16 cm , e ) 18 cm
[A]:
c