Does it have a connector for a wired Ethernet connection?
Or maybe your cable modem has USB output. In that case, the tablet should have USB and a driver to communicate with the cable modem via USB (just like you installed on your laptop/PC to get it working).
If not, a WiFi router seems the only solutiuon. Or a 3G/4G 'dongle' to use the wireless AT&T or Verizon network in stead of the cable.
do not have wifi in this location