A conducting sphere has a net charge of - 6.4 * 10-17

c. What is the approximate number of excess electrons on the sphere?

The charge of a single electron is - 1.6 x 10^ (-19) C. To figure out the total number of excess electrons, divide the net charge by the charge of a single electron:

-6.4 x 10^ (-17) / - 1.6 x 10^ (-19) = 400

There are about 400 excess electrons on the sphere.