Question 1079993
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The normal force produced by 15 kg mass is m*g = 15*9.81 = 147.15 N (newtons)

The kinetic friction coef. = {{{22/147.15}}} = 0.15.   CORRECT !!


In the next step (in the Part 2) you need to use the mass of 15 kg + 40 kg + 65 kg.
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