Answer
241 mmHg
Work Step by Step
$P_{1}=685\, mmHg$
$V_{1}=15.0\,L$
$T_{1}= (25+273)K= 298\,K$
$T_{2}= (-35+273)K=238\,K$
$V_{2}=34.0\,L$
Combined gas law is
$\frac{P_{1}V_{1}}{T_{1}}=\frac{P_{2}V_{2}}{T_{2}}$ (if n is constant)
$\implies P_{2}=\frac{P_{1}V_{1}T_{2}}{T_{1}V_{2}}$
$=\frac{685\, mmHg\times15.0\,L\times238\,K}{298\,K\times34.0\,L}=241\,mmHg$