How do you solve this word problem?

Question

A child is running on a moving sidewalk in an airport. When she runs against the sidewalk's motion, she travels 90ft in 15 seconds. When she runs with the sidewalk's motion, she travels 70ft in 7 seconds. What is the rate of the child on a still sidewalk and what is the rate of the moving sidewalk?

Answer 1

 

 Against :    6 ft / sec

 

 With: 10 ft/ sec

 

 

Let S be the speed of the moving sidewalk and R be HER speed running

(R+s) = 10

(R-s) = 6  

 

2R = 16

 

R=8 ---> S = 2

 

She runs 8 feet per second and the sidewalk moves 2 feet per second