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
