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: calculate the speed of a boat in still water ( in km / hr ) if in one hour , the boat goes 10 km / hr downstream and 4 km / hr upstream . 
Options: a ) 7 kmph , b ) 8 kmph , c ) 9 kmph , d ) 7 kmph , e ) 6 kmph
a

Problem: a bicycle wheel has a diameter of 0.51 m . how many complete revolutions does it make in 1 km ? 
Options: a ) 246 , b ) 448 , c ) 1408 , d ) 710 , e ) 624
e

Problem: a can do a piece of work in 20 days . when he had worked for 2 days b joins him . if the complete work was finished in 8 days . in how many days b alone can finish the work ? 
Options: a ) 18 , b ) 77 , c ) 66 , d ) 55 , e ) 10

e