The task is to generate the correct answer for a given math problem.

Problem: if x , y , and z are positive integers , and 3 x = 5 y = 6 z , then the least possible value of x + y + z is
21

Problem: audrey 4 hours to complete a certain job . ferris can do the same job in 3 hours . audrey and ferris decided to collaborate on the job , working at their respective rates . while audrey worked continuously , ferris took 5 breaks of equal length . if the two completed the job together in 2 hours , how many minutes long was each of ferris ' breaks ?
6

Problem: a train of 25 carriages , each of 60 meters length , when an engine also of 60 meters length is running at a speed of 60 kmph . in what time will the train cross a bridge 1.0 km long ?
2.5