a balloon of gross weight w N descends with an accelaration a m/s^2 . the weight that must be thrown out in order to give the balloon an equal upward accelaration will be

if the baloon weight w and it desend. if we will fall the w'' weight from the baloon then we find (w-w'')g force towards downwards and upward accelaration is wa .

                                                                 hence we have a equation (w-w'')g=wa    

                                                                     a=(w-w'')g/w