I'm so confused... please help me. Even if you don't answer the question just explain it, lay it out plainly a preferably a step-by-step solution.

Q:
The dome of a van de Graff generator carries a negative charge of 8.0 x 10-7C.
How many excess electrons does it posses? What is the increase in mass because of their presence?

It sounds like science, it's simple. You should have a formula for these things, so start there, lay out what you have and go from there then you will get the answer, I have science I love it!! And if you have a picture, don't read the question it confuses you, that's what my teacher tells us and trust it works... good luck