$V=10.0mL$
$\pi$=13.3mm Hg
$\Rightarrow \large\frac{13.3}{760}$ atm
$T=25^{\large\circ}C=25+273=298K$
R=0.0821L atm mol$^{-1}K^{-1}$
Molar mass $M=\large\frac{WRT}{\pi V}$
$\Rightarrow \large\frac{0.1\times 0.0821\times 298}{\Large\frac{13.3}{760}\normalsize\times 0.01}$
$\Rightarrow \large\frac{0.10\times 0.0821\times 298\times 760}{13.3\times 0.01}$
$\Rightarrow \large\frac{1859.4008}{0.133}$
$\Rightarrow 13980.4 g mol^{-1}$