see when u draw the free body diagram and write the condition of equilibrium u will get the equation

solving this u will get the value

                                               x = 26.79 cm

and this is the required answer.

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simple yaar resolve the wt. of 2nd body along the plane that should be equal to electrostatic force.

now caliculate for r

for the body to be in equilibrium

on substituting the given values u will get

x = 0.271 m

i.e.

x = 27.1cm