Answer
$X_{He}=0.440$
$X_{Ar}=0.299$
$X_{Xe}=0.261$
Work Step by Step
$P_{total}= P_{He}+P_{Ar}+P_{Xe}$
$=0.467\,atm+0.317\,atm+0.277\,atm$
$=1.061\,atm$
For a gas A, mole fraction $X_{A}=\frac{P_{A}}{P_{total}}$
Then, $X_{He}=\frac{P_{He}}{P_{total}}=\frac{0.467\,atm}{1.061\,atm}=0.440$
$X_{Ar}=\frac{P_{Ar}}{P_{total}}=\frac{0.317\,atm}{1.061\,atm}=0.299$
$X_{Xe}=\frac{P_{Xe}}{P_{total}}=\frac{0.277\,atm}{1.061\,atm}=0.261$
