The answer would be 20 miles. Do a proportion, 5/40= x/160. Cross multiply and divide. 5 x 160= 800, 800 divided by 40= 20. Now you can also look at it like this 5 miles= 40 minutes. This means every 40 minutes they have done 5 miles. 40 goes into 160 four times. 5 x 4= 20