If 18, persons can build a 140m long wall in 42 days, the number of days that 30 persons will take to complete a similar 100m long wall is :

1)  18

2)  21

3)  24

4)  28

Train 'A' leaves Mumbai Central Station for Lucknow at' I1 a.m. running at the speed of 60 kmph. Train 'B' leaves

Mumbai 'Central station for Lucknow by the ,same route at 2 p.m. on the same day . running. at the speed of 72 kmph

 At what time will the two trains meet each other?

1) 3 a.m. on the next day

2) 5 a.m. on the next day

3) 5 p.m. on the next day

4) 3 p.m. on the next day