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
