Suppose ideal gas equation follows $ VP^3 = constant$ , Initial temperature and volume of the gas are T and V respectively. If gas expand to 27 V, then temperature will become
$ VP^3 = constant = k \Rightarrow P^3 \alpha { 1 \over V} \Rightarrow P \alpha { 1 \over V^{1 /3 }} \Rightarrow P = {k \over V^{1/3} } $ $ PV = RT \Rightarrow { k \over V^{1/3 }}V = RT $ $ = k V^{2/3 } = RT $ $ = V^{2/3} = RT/ k $ $ Hence \left( { V_1 \over V_2 } \right)^{2/3} = { T_1 \over T_2} \Rightarrow \left( { V \over 27V } \right)^{2/3} = { T \over T_2 } $ $ \Rightarrow {1 \over 9 } = { T \over T_2} \Rightarrow T_2 = 9T $