A long container has air enclosed inside at room temperature and atmospheric pressure ${\text{(10}}^{\text{5}}\text{pa)}$   . It has a volume of 20,000 cc. The area of cross section is ${\text{100 cm}}^2$  and force  constant of spring is ${\text{k}}_{\text{spring}}=\text{1000N/m}$  . We push the right piston isothermally and  slowly till it reaches the original position of the left piston which is movable. What is  the final length of air column in m. Assume that spring is initially relaxed.