(20) 3. The 6-kg hanging mass A is attached to a pulley that hangs on a rope that passes over a pulley to connect to the 9-kg hanging mass B. a) Write an equation for the length \( \ell \) of the rope in terms of the height H, the height of mass A - \(s_A\), and the height of mass B - \(s_B\). b) Find the acceleration of each mass, clearly stating whether the acceleration is upward or downward.