Answer: the cyclist's speed during the first portion is 13 mph and his speed during the cool down portion is 9 mph.
Explanation:
Let x represent the cyclist's speed during the first portion.
The cyclist rode the first 26-mile portion of his workout at a constant speed.
Time = distance/speed
Time taken to ride through the first portion is
26/x
For the 18-mile cool down portion of his workout, he reduced his speed by 4 miles per hour. It meas that his speed during the cool down portion is (x - 4) mph. Time taken to ride through the cool down portion is
18/(x - 4)
Since each portion of the workout took the same time, it means that
26/x = 18/(x - 4)
Cross multiplying, it becomes
26(x - 4) = 18x
26x - 104 = 18x
26x - 18x = 104
8x = 104
x = 104/8
x = 13 mph
His speed during the cool down portion is
13 - 4 = 9 mph