Answer
Please see the work below.
Work Step by Step
We know that
$Total\space moles=0.31+0.25+0.29=0.85 \space moles$
$Total\space pressure=1.5 \space atm$
We also know that $Partial\space pressure=mole\space fraction\times total \space pressure$
$P_{CH_4}=\frac{0.31}{0.85}\times 1.5atm=0.54atm$
$P_{C_2H_6}=\frac{0.25}{0.85}\times 1.5atm=0.445atm$
$P_{C_3H_8}=\frac{0.29}{0.85}\times 1.50=0.505atm$
