Use of USB cable for 20Mbps Internet?

I am thinking of upgrading my internet to 20Mbps, but the home network that I have set up uses a USB cable to run from the modem to the main pc. It is only a small network (2 Computers), But can a USB cable handle 20 Megabits of bandwidth? And does anyone know how fast 20Mb per second is in Kilobits?

Thanks
 
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