Answer:
Step-by-step explanation:
Let the distance the slower hiker travels=d,
the distance the faster hiker travels=15-d (Since, the sum of the distances they walk is 15mi).
Let the speed of the slower hiker in mi/hr=s,
the speed of the faster hiker=s+0.5
Now, equation for the slow hiker:

(1)
and equation for the faster hiker:


(2)
Now, substituting the equation (1) in equation (2),



and 
The speed of the slower hiker is
and The speed of the faster hiker is
.