Can you explain stoichiometry to me?

Stoichiometry is a bit hard to explain through here but this is a link to a site that can teach it to you better than somebody on here could.

http://www.chem4kids.com/files/react_stoichio.html

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)

You would do 1500/4 and the answer is 375