Two small spheres spaced 35cm apart have equal charge how many excess elecotrons must be present on each sphere if the magnitude of the force of repulsion between them is 2.20x10-21n?

After the near spacecraft passed mathilde, on several occasions rocket propellant was expelled to adjust the spacecraft's momentum in order to follow a path that would approach the asteroid eros, the final destination for the mission. after getting close to eros, further small adjustments made the momentum just right to give a circular orbit of radius 45 km (45 × 10^3 m) around the asteroid. so much propellant had been used that the final mass of the spacecraft while in circular orbit around eros was only 545 kg. the spacecraft took 1.04 days to make one complete circular orbit around eros. calculate what the mass of eros must be.

An object moves from the position +34m to the position -15m in 15 seconds. what is it's total displacement? what is it's average velocity?

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.