My annual salary will be 55k$.But I will be in us (detroit) for 3 months only. How much Tax I have to pay. Will there be any tax exemption if I bring my wife and chile (less than 1 year old).

1. There is different treatment if it is income from salary or income as independent contractor.
2. Say less than 89 days, more than 89 days but less than 183 days.
3. Your visa type. On this depends if your income is subject to FICA taxes or not.
4. You will file nonresident tax return. You will only get your personal exemption ($3,500 in 2008). You don't get exemption for your spouse and child.

Read about nonresident tax filing: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents