Answer:
 fr ’= ½ F
Explanation:
For this exercise we use the translational equilibrium equation, on the axis parallel to the wall
       fr - W = 0
       fr = W
for the adult man they indicate that the friction force is equal to F
       F = M g
we write the equilibrium equation for the child
       fr ’= w’
       fr ’= m g
in the statement they tell us that the mass of the adult is 2 times the mass of the child
       M = 2m
we substitute
      fr ’= M / 2 g
      fr ’= ½ Mg
we substitute
      fr ’= ½ F
therefore the force of friction in the child is half of the friction in the adult