The ball has an initial speed of 10m/s. This is because it is moving with the balloon. Now the balloonist throws the ball 4m/s with respect to himself, so it means that he gives the ball a extra push of 4m/s, so the total speed is 14m/s. Since it takes 30 seconds to reach the ground, the distance travelled is 14*30=420m.
I could be wrong, but I'm pretty sure it's 144kg.
The change in electric potential energy of the ion is equal to the charge multiplied by the voltage difference:

where the charge q of the na+ ion is equal to one positive charge, so it's equal to the proton charge:

, and Vf and Vi are the final and initial voltages.
Substituting the numbers, we find: