Am I doing this right? electricity?

I'm trying to use an 18V, 1.7 Amp, 30.6 Watt battery to power a 5V, 0.5 Amp, 2.5 Watt USB port using a resistor on a printable circut board. if my calculations are correct, the battery is 10 ohms and the USB port is 10 ohms. This doesn't seem right to me. If that is not right, can you please tell me where I went wrong? And what kind of resistor should I be using? Like how much resistance?