I am filing Form 843 for withheld medicare & social security taxes( for 2012) as my employer has asked me to file the claim with IRS.

What should I write in:

1) Line 3: Type of tax or fee?
Should I write employment or income?
While some people say employment but in this article it says income.

2) Do I need to fill 5a & 5b?
If yes what should be the option?

Options for 5a:
1)Interest was assessed as a result of IRS errors or delays.
2)A penalty or addition to tax was the result of erroneous written advice from the IRS.
3)Reasonable cause or other reason allowed under the law (other than erroneous written advice) can be shown for not assessing a penalty or addition to tax.

5b : Date(s) of payment(s) ___________________________

3) Line 6 : Original return :
What should I write here: 941 or 1040 NR-EZ

And if I am not wrong I have to send these documents with form 843:
1) copy of my Passport showing F1 visa
2) Copy of my I-94
3) Copy of my W2
4) Form 8316

Please tell me if I am missing anything.

Thank you very much in advance for your help

Read about filing Form 843: Your U.S. Tax Return: Social Security and Medicare (FICA) Taxes for Non-resident Exempt Individual