Answer
$8.3\times10^{-3}\,g$
Work Step by Step
$\Pi= M\times RT\implies M=\frac{\Pi}{RT}$
$=\frac{0.015\,atm}{0.08206\,L\,atm K^{-1}mol^{-1}\times298\,K}$
$=6.134\times 10^{-4}\,mol/L$
Moles of urea=
$6.134\times10^{-4}\,mol/L\times0.225\,L$
$=1.38\times10^{-4}\,mol$
Mass of urea= $1.38\times10^{-4}\,mol\times60.06\,g/mol$
$=8.3\times10^{-3}\,g$