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 car traveling at a certain constant speed takes 10 seconds longer to travel 1 km than it would take to travel 1 km at 80 km / hour . at what speed , in km / hr , is the car traveling ? 
Options: a ) 70 , b ) 72 , c ) 74 , d ) 65 , e ) 78
d

Problem: a river boat leaves silver town and travels upstream to gold town at an average speed of 6 kilometers per hour . it returns by the same route at an average speed of 5 kilometers per hour . what is the average speed for the round - trip in kilometers per hour ? 
Options: a ) 5.5 , b ) 7.1 , c ) 7.2 , d ) 7.0 , e ) 8.0
a

Problem: mahesh can do a piece of work in 45 days . he works at it for 20 days and then rajesh finished it in 30 days . how long will y take to complete the work ? 
Options: a ) 54 , b ) 25 , c ) 37 , d ) 41 , e ) 30

a