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: walking with 4 / 5 of my usual speed , i arrive at the bus stop 7 minutes later than normal . how many minutes does it take to walk to the bus stop at my usual speed ? 
Options: a ) 12 , b ) 16 , c ) 20 , d ) 24 , e ) 28
e

Problem: a train 120 m in length crosses a telegraph post in 6 seconds . the speed of the train is ? 
Options: a ) 72 kmph , b ) 88 kmph , c ) 54 kmph , d ) 18 kmph , e ) 19 kmph
a

Problem: abel can complete a work in 8 days , ben in 12 days and carla in 15 days . all of them began the work together , but abel had to leave after 2 days and ben 3 days before the completion of the work . how long did the work last ? 
Options: a ) 4 , b ) 7 , c ) 8 , d ) 9 , e ) 10

a