A Balloon contains $1500m^3$ of $He$ at ${27}^{o}C$ and 4 atmospheric pressure, the volume of $He$ at $-3^{o}C$  temperature and 2 atmospheric pressure will be

Given, initial volume, temperature and pressure be  
 $V_1,T_{1}and p_{1}are 1500m^3,{27}^{o}C and4atm$
Final volume, temperature and pressure are  $V_2,T_{2}and{p}_2$ are 
 $V_2,-3^{o}Cand 2atm$
By using ideal gas equation 
$pV=nRT=\frac{pV}{T}=cons\tan t\Rightarrow \frac{p_1{V}_1}{T_1}=\frac{p_2{V}_2}{T_2}\Rightarrow V_2=\frac{p_1{V}_1{T}_2}{T_1{p}_2}$

$\therefore V_2=\frac{4\times 1500\times 270}{300\times 2}=2700m^3$