Answer
$P=0.378\ atm$
Work Step by Step
Initial concentration: $0.05\ mol\div 12.5\ L=0.004\ M$, reacted concentration: x
$K_c=[CO][Cl_2]/[COCl_2]$
$0.0071=x\times x/(0.004-x)$
$x^2+0.004x-2.84\times10^{-5}=0$
$x=0.00369$
Total concentation: $x+x+(0.004-x)=0.00769\ M$
Pressure:
$P=CRT$
$P=0.00769\ M\times 0.082\ atm/M.K\times600\ K=0.378\ atm$
