All the surfaces & pulleys are frictionless in the shown arrangement. Pulleys P and Q are massless. The force applied by clamp on pulley P is 

$$\begin{gathered} 2mg\sin 30-T=2m\left(a\right) \\ \mathrm{T}=\mathrm{ma} \\ \Rightarrow \mathrm{a}=\mathrm{g}/3\mathrm{\&}\mathrm{T}=\frac{\mathrm{mg}}{3} \\ \therefore \mathrm{Net} \mathrm{force} = \end{gathered}$$
Result of these forces $=\mathrm{T}(-\widehat{\mathrm{j}})+\mathrm{Tcos}{60}^{\circ }(-\widehat{\mathrm{j}})+\mathrm{Tsin}60(-\widehat{\mathrm{i}})$
$$\begin{gathered} =-\frac{\sqrt{3}}{2}\mathrm{T}\widehat{\mathrm{i}}-\frac{3}{2}\mathrm{T}\widehat{\mathrm{j}} \\ =\frac{\mathrm{mg}}{6}(-\sqrt{3}\widehat{\mathrm{i}}-3\widehat{\mathrm{j}}) \end{gathered}$$
As net force in pulley = 0,
$\text{ force by clamp }=\frac{mg}{6}(\sqrt{3}\widehat{i}+3\widehat{j})$