Consider two points from which two persons start walking towards each other. They cross each other after time T1. They went further to the opposite points and return instantaneously to cross each other again after time T2. Then T2 =
2T1
Suppose the distance between the two points is 'd'.
When the persons meet for the first time, total distance covered = d
When persons meet for the second time, total distance covered = d + 2d
Distance = d, time taken = T1; distance = 2d, time taken = 2T1 = T2
Hence Option (a)
Alternative Approach: Using Assumption
You can also solve this using numbers. If the distance is 100 km, and the speed is 50 kmph for each person, they will meet after 12 an hour. They will reach the opposite corners in 1 hour and will meet again in 112 hours; thus T2=1 hour = 2T1. Option (a)