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'.

[EX Q]: Problem: 28 machines can do a work in 10 days . how many machines are needed to complete the work in 40 days ? 
Options: a ) 10 , b ) 6 , c ) 4 , d ) 7 , e ) 5
[EX A]: d

[EX Q]: Problem: the speed at which a man can row a boat in still water is 15 km / hr . if he rows downstream , where the speed of current is 3 km / hr , how many seconds will he take to cover 90 meters ? 
Options: a ) 12 , b ) 16 , c ) 17 , d ) 18 , e ) 20
[EX A]: d

[EX Q]: Problem: the speed of a boat in still water in 26 km / hr and the rate of current is 6 km / hr . the distance travelled downstream in 20 minutes is : 
Options: a ) 10.4 km , b ) 10.66 km , c ) 11.4 km , d ) 11.22 km , e ) 12 km
[EX A]:
b