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'.

Problem: a boat covers a certain distance downstream in 1 hour , while it comes back in 1 ½ hours . if the speed of the stream be 3 kmph , what is the speed of the boat in still water ? 
Options: a ) 12 kmph , b ) 13 kmph , c ) 14 kmph , d ) 15 kmph , e ) none
d

Problem: if 42 men do a work in 25 days , in how many days will 50 men do it ? 
Options: a ) 23 , b ) 22 , c ) 19 , d ) 20 , e ) 21
e

Problem: a mobile battery in 1 hour charges to 20 percent . how much time ( in minute ) will it require more to charge to 30 percent . 
Options: a ) 145 , b ) 90 , c ) 175 , d ) 160 , e ) 130

b