The final charge on each of the three separated spheres in part (b) is +3.0 μc. how many electrons would have to be added to one of these spheres to make it electrically neutral?

electrons should be added to one of these spheres to make it electrically neutral.

Explanation:

Total charge on each sphere =  +3.0 μC =

In order to neutralize the positive charge equal magnitude of negative charge is to be added.

Total charge electrons, Q=  -3.0 μC =

Number of electrons = n

Charge on a single electron, e =

Q = n × e

electrons should be added to one of these spheres to make it electrically neutral.