The change of state that is occurring is from the liquid state to the solid state.
Explanation :
The forces acting on hot- air balloon are:
Weight, (W)
Force due to air resistance, (F)
Upthrust force, (U)
Its weight W is acting in downward direction. The upthrust force U acts in upward direction. When the balloon is moving upward, the air resistance is in downward and vice versa.
In this case, the hot-air balloon descends vertically at constant speed.
so, 
and 
so,
....................(1)
when it is ascending let the weight that it is releasing is R, so
..........(2)
solving equation (1) and (2)

2F is the weight of material that must be released from the balloon so that it ascends vertically at the same constant speed.
I’ve answered this before so I know the question is missing an
important given and that given is: <span>1 has an
empty trailer and the other has a fully loaded one.
So, it would be the fully loaded trailer that would take a longer distance to
stop because a lot of weight is being pulled, and when the brakes are started,
the fully loaded trailer is more like pushing against the truck.</span>