12) Find the mass M if the hanging block shown in figure. Which will prevent the smaller block from slipping over the triangular block. All the surfaces are frictionless and the strings and the pulleys are light.
$$\begin{gathered} \left(1\right) \frac{m+M_1}{(\sin \theta -1)} \\ \left(2\right) \frac{m+M_1}{(\cos \theta -1)} \\ \left(3\right) \frac{m+M_1}{(\tan \theta -1)} \\ \left(4\right) \frac{m+m_1}{(\mathrm{co}t \theta -1)} \end{gathered}$$