The partial pressure  for the gases is as below
CHâ‚„=0.547 Â atm
C₂H₆= 0.441 atm
C₃H₈ =0.512 atm
calculation
 partial  pressure of a  gas=[ (moles  of the gas/ total  moles) x  total pressure]
Total  moles = moles of (  CH₄ + C₂H₆ + C₃H₈)  =0.31 + 0.25 +0.29 = 0.85  moles
Total pressure = 1.5 atm
partial pressure  for CH₄ = (0.31/0.85)  x 1.5 atm=0.547 atm
Partial  pressure for C₂H₆ =( 0.25 /0.85)  x 1.5 atm = 0.441 atm
partial  pressure for C₃H₈ =(0.29/0.85)  x 1.5 atm =0.512 atm