A hot-air balloon has a total mass of 740kg. It accelerates downwards (towards the ground) at 1.9m/s2 even though an upwards lift force in acting on it.

a) Find the lift force acting on the balloon: 

b) What must be the total mass that needs to be thrown overboard if the operator on the hot-air balloon decides to accelerate upwards at 3.7m/s2? Assume the upwards lift force remains the same.