From your annual income of $78,000.00, assuming that you're single, your estimate annual net pay or take home will be $55,618.50. Figures may change depending on your status and tax code.
The table below shows the tax brackets for 2014:
Of interest, the Tax Institute of H&R Block calculated the 2013 federal income tax bill of a dual-earner married couple with two young kids and compared it to the tax bill of a single person without kids. They found out that the single person paid much higher taxes. See a detailed comparison at CNN Money.