How long does it take to remove the rear wheels, remove the axles, unbolt the calipers, remove the pads, remove the hubs, remove the rotors, turn the rotors, reinstall the rotors, replace the hub seals, reinstall the hubs, reinstall the axles, install new pads, reinstall the calipers, and remount the wheels? The front brakes take less time of course, with half the wheels and no axles to remove. Include time to road test the finished work, multiply by the hourly labor rate, and then add on the retail price for the parts, shop supplies, taxes, etc.