Marcus can walk 1 mile to the library in the same time he can bicycle 2.5 miles to the sporting goods store. his speed on the bicycle is 6 mi/h faster than his walking speed. what is his speed walking?

Let
x> speed on the bicycle
y> speed walking

we know that
x=6+y> equation 1
speed=distance /time> time=distance/speed
1/y=2.5/x> y=x/2.5> x=2.5y> equation 2

equals 1 and 2
6+y=2.5y> 2.5y-y=6> 1.5y=6> y=6/1.5> y=4 mi/h
x=6+y> x=6+4> x=10 mi/h

the answer is
the speed walking is 4 mi/h