Explanation:
If \(T\) is the tension in the rope, then the force exerted by the boy \(B\) on the rope is equal to the force exerted by the rope on the boy. Let \(R\) be the normal reaction between the boy and the frame.
The free body diagrams of boy and frame are shown in figures (a) and (b) respectively.

From the free body diagram of boy
\(T + R = 40\;g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( 1 \right)\)
From the free body diagram of frame
\(T = R + 360\,g\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\rm{ }}\,\,\,\,\,\,\left( 2 \right)\)
Adding (1) and (2), we get
\(2T = 400\;g\,{\rm{or}}\,T = 200\;g\)