$\left( P _{ A }\right)_{30 \min }=\left( P _{ A }\right)_0\left(\frac{1}{2}\right)^{30 / 10}$
$\left( P _{ A }\right)_{30 \min }=100\,mm\,Hg$
$A ( g ) \rightarrow 2 B ( g )+ C ( g )$
$\begin{array}{lccc}\text { at } t =0 & 800\,mm & 0 & 0 \\ \text { at } t =30 & 100\,mm & 1400\,mm & 700\,mm \end{array}$
Total pressure after $30$ minutes $=2200\,mm\,Hg$