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: a rower can row 5 km / h in still water . when the river is running at 2 km / h , it takes the rower 1 hour to row to big rock and back . how many kilometers is it to big rock ?
Options: a ) 1.5 , b ) 1.8 , c ) 2.1 , d ) 2.4 , e ) 2.7
[EX A]: c

[EX Q]: Problem: if 12 men do a work in 80 days , in how many days will 16 men do it ?
Options: a ) 22 , b ) 87 , c ) 77 , d ) 60 , e ) 85
[EX A]: d

[EX Q]: Problem: if the population of a certain country increases at the rate of one person every 45 seconds , by how many persons does the population increase in 1 hour ?
Options: a ) 80 , b ) 120 , c ) 150 , d ) 180 , e ) 160
[EX A]:
a