Grammar Questions...

1. How do you write in a formal essay the money number? spelled out or just put the number

2. Do i have to put a comma after an and whaen im writting about more than three things in the same sentance?

3. Should I spell out US in a formal essay?

Animal experimentation Article from PETA

Animals are not our to experiment on!!
http://www.petaasiapacific.com/issues-nottoexperiment.asp