A balloon of mass M is stationary in air. It has a ladder on which a man of mass m is standing. If the man starts climbing up the ladder with a velocity v relative to the ladder, the velocity of the balloon is

Question

$$\begin {array} {1 1} (a)\;\frac{m}{M}v \;upwards & \quad (b)\;\frac{mv}{(m+M)}\;downwards \\ (c)\;\frac{mv}{(m+M)}\;upwards & \quad  (d)\;\frac{Mv}{(M+m)}\;downwards \end {array}$$