Question regarding force in the vertical direction?

A research balloon of total mass 420 kg is descending vertically with a downward acceleration of 2.8 m/s2. How much ballast must be thrown from the car to give the balloon an upward acceleration equal to 2.3 m/s2, presuming that the upward lift of the balloon does not changeQuestion regarding force in the vertical direction?
net F = m*a = weight + lift

lift = Fnet - Fw

Fl = m*a - m*g = m(a-g) = 420(-2.8 - (-9.8)) = 420*7.0 = 2940 N

the lift remains the same

so we may now calculate the new mass



Fl = m(a-g)

2940 = m(+2.3 - (-9.8)) = m(12.1)

m = 243 kg



original m = new m + ballast dumped

420 = 243 + m

m ballast = 177 kg