A first order gas phase reaction A $->2$R $+$ S is conducted under isothermal,

isobaric condition in a piston type batch reactor. At t $=0$ min, the molar

percentage of A is $75\%$ while the molar percentage of an inert gas is $25\%.$

After $8$ mins, the volume of the reaction is doubled.

$1)$What is the conversion of A at t $=8$ mins?