A. Social security is taxed at 6.2% of "social security wages," which includes your base wages plus the cost of certain employee benefits that your employer may be providing you (life insurance, for example) minus pre-tax contributions to your retirement plan and medical insurance plans. SS tax applies on your first $106,800 of wages in 2009.
B. Medicaire is taxed at 1.45% of social security wages. There is no limit on this.
C. Federal income tax is withheld at a rate commensurate with your wage rate and with the number of allowances you specified when you submited your W-4 to your employer. There are several methods your employer may use to determine the amount to withhold, depending on whether you are paid weekly, semi monthly, or monthly. You can learn all the gory details here:
http://www.irs.gov/pub/irs-pdf/p15.pdf
http://www.irs.gov/pub/irs-pdf/p15a.pdf
Go to page 24 of pub 15-A for the withholding tables.
D. Here is a calculator for determining the withholdng for VA:
Virginia Department of Taxation
Your employer also pays the same amount as you to the IRS for SS and medicaire tax payments (i.e, 7.65% of your salary).
As for how much your employer pays for your medical and dental insurance - you'll have to ask your employer that.
Whether your employer pays corporate income tax - to either the US or DC - depends on their profits. Few corporations make this info public. You can get an idea from the annual report if you work for a publically held company, but be aware that what's stated in the annual report is typically not what they actually pay, due to issues such as different depreciation amounts stated in the annual report versus what they report to the IRS.
I don't follow what you mean by "30% of 100$ to my employer" - please clarify. If your pay rate is $100/hour, and they withhold $30, NONE of that money goes to your employer - it all goes to pay taxes or to the medical insurance carrier. In addition, your employer must also pay an additional $7.65 as their contribution for SS and medicaire. As for corporate tax - if they are taxed at 30% of profits (just a guess), the money they pay you and their contributions for your medical insurance are considered to ne expenses, which reduce their profit, and hence also reduces their income tax liability. Does this help?