A balloon of mass 30 kg is falling down with an acceleration of $1.8m/s^{-2}$.Then some mass is removed from the balloon.As a result the balloon moves upwards with an acceleration of $2.2 ms^{-2}$. The mass removed from the balloon is
$(a)\;16 kg\quad (b)\;10 kg \quad (c)\;18 kg \quad (d)\;12 kg$