b
$PV = mrT = P \propto mT$
$\Rightarrow$ $\frac{{{P_1}}}{{{P_2}}} = \frac{{{m_1}}}{{{m_2}}} \times \frac{{{T_1}}}{{{T_2}}}$
$\Rightarrow$ $\frac{{10}}{{{P_2}}} = \frac{m}{{m/2}} \times \frac{{(273 + 27)}}{{(273 + 87)}}$
$\Rightarrow$ ${P_2} = 6\,atm$