A rope ladder of length L is attached to a balloon of mass M. As the man of mass m climbs the ladder into the balloon basket, the balloon comes down by a vertical distance s. Then the increase in potential energy of man divided by the increase in potential energy of balloon is 

Work done by man,  $\mathrm{mgL}=\mathrm{mg}(\mathrm{L}-\mathrm{s})+\mathrm{mgs}$

where mg(L - s) is the increase in potential energy of the man and mgs is the increase in potential energy of the balloon because the balloon would have been lifted up but for the climbing of the man. So
$\frac{\text{ Increase in }\mathrm{PE}\text{ of }\mathrm{man}}{\text{ Increase in PE of baloon }}=\frac{\mathrm{mg}(\mathrm{L}-\mathrm{s})}{\mathrm{mgs}}-\frac{\mathrm{L}-\mathrm{s}}{\mathrm{s}}$