Alright, lets get started.
Suppose first bicyclist speed is = x mph
As given in question, second one is 4 mph slower than first, hence
Speed of second bicyclist is = (x-4) mph
They both travels 3 hrs so,
distance covered by first bicyclist :


distance covered by second bicyclist :

4 miles were still left after 3 hrs of driving.
It means they covered 88 - 4 = 84 miles together



Adding 12 in both sides


Dividing 6 in both sides


Means speed of first bicyclist = 16 mph
Speed of second bicyclist =
mph
Hence speed of both bicyclist are 16 mph and 12 mph. : Answer
Hope it will help :)