Physics
posted by Lindsay .
A research balloon of total mass 200 kg is descending vertically with a downward acceleration of 3.2 m/s^2. How much ballast must be thrown from the car to give the balloon an upward acceleration equal to 2.8 m/s^2, presuming that the upward lift of the balloon does not change?
Could someone at least show me the first steps? I don't even know where to begin.

The upward lift is constant, it depends only on the size of the balloon.
netforce= mass*acceleration
Liftmg=m*a
liftg(mdeltam)=(mdeltam)*newacc
1)solve for lift in the original equation, knowing m, a, and g.
2) solve for deltamass in the second equation knowing lift, g, m, and the new acceleration. 
For lift I got 1320, and for deltamass I got 304.76. Is this right? If so, do I have to add those to the netforce?