Answer: Marcus's walking speed is 4 mph
Explanation:
Let x represent Marcus's walking speed.
His speed on the bicycle is 6 mi/h faster than his walking speed. This means that his speed on the bicycle would be
x + 6
Time = distance/speed
Time spent by Marcus in walking 1 mile to the library is
1/x
Time spent by Marcus in bicycling 2.5 miles to the sporting good store is
2.5/(x + 6)
Since the time that he spends in walking to the library is about the same time that he spends in bicycling to the sporting good store, then
1/x = 2.5/(x + 6)
Cross multiplying, it becomes
1 × (x + 6) = 2.5 × x
x + 6 = 2.5x
2.5x - x = 6
1.5x = 6
x = 6/1.5 = 4