The Volumes can be calculated from Masses by using following Formula,
Density = Mass / Volume
Solving for Volume,
Volume = Mass / Density
Mass of Both Gases = 14.1 g
Density of Argon at S.T.P = 1.784 g/L
Density of Helium at S.T.P = 0.179 g/L
For Argon:
Volume = 14.1 g / 1.784 g/L
Volume = 7.90 L
For Helium:
Volume = 14.1 g / 0.179 g/L
Volume = 78.77 L