Question 1078299
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c + s = 132/11   (1)   (the rate traveling with sidewalk)
c - s = 60/15    (2)   (the rate traveling against sidewalk)

Or

c + s = 11,      (1')
c - s =  4       (2')

Add (1') and (2'):

2c = 15  --->  c = {{{15/2}}} = 7.5 ft per second is the rate of the child on a still sidewalk.

===>  s = 11-7.5 = 3.5 ft per second is the rate of sidewalk.
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