Physics electrical charge problems?

[cat_eyes]

1) Two conducting spheres have identical radii. Initially they have charges of opposite sign and unequal magnitudes with the magnitude of the positive charge larger than the magnitude of the negative charge. They attract each other with a force of 0:225 N when separated by 0:4 m. The spheres are suddenly connected by a thin conducting wire, which is then removed.
Now the spheres repel each other with a force of 0:046 N. What is the magnitude of the positive charge? Answer in units of C.

2) What is the negative charge? Answer in units of C. (refer to question 1 for details)

3) Calculate the gravitational force between two electrons that are .57 cm apart. Answer in units of N.