After 1 hour they meet.
Step-by-step explanation:
Distance between them = 6 miles
Speed of uphill person = 2.5 miles per hour
Speed of downhill person = 3.5 miles per hour
Relative velocity = 2.5 - ( -3.5 ) = 6 miles per hour
We know
Displacement = Velocity x Time
6 = 6 x Time taken
Time taken = 1 hour
After 1 hour they meet.