Two locomotives approach each other on parallel tracks. each has a speed of 155km/h with respect to the ground. if they are initially 8.5 km apart. how long will it be before they reach each other

They're initially 8.5 km apart.

The open space between them is shrinking at the rate of 155 km/hr
from one end, and 155 km/hr from the other end, so the space is
closing at the rate of  310 km/hr.

The open space between them will shrink to zero in

               (8,500 m) / (310,000 m/hr) 

           =           0.02742 of an hour

           =             98.7 seconds   

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