Given in the figure are two blocks A and NB of weight $20\;N$ and $100\;N$ respectively . These are being pressed against a wall by a force F as shown. If the coefficient of friction between the blocks uis $0.1$ and between block B and the wall is $0.15$ , the frictional force applied by the wall on block B is :

Question

$\begin{array}{1 1} 150\;N \\ 100\;N \\ 80\;N \\ 120\;N \end{array} $