enable business public wifi

No. The only devices capable of Comcast's "xfinitywifi" scheme are the rented wireless gateways (Cisco DPC3939B or DPC3941B).

However, your R6400 does have a "guest network" feature that you can enable. This will allow you to offer free WiFi, with the added benefit of NOT having to be a Comcast customer to use it. (The "xfinitywifi" offers free wifi IF you are a Comcast subscriber; if not, then it is free for 30 minutes at a time, with payment required after that.)

Thanks for quick reply... You answer is what I was expecting.. I have the guest  wifi enabled on the r6400 now but it doesnt have a good way of limiting  bandwidth & was thinking the xfinity wifi may be a better way to go..Thanks again, wildherre

Yeah, you may need a more advanced router to be able to limit guest bandwidth. I believe the ASUS RT-xxxx line can do this (if the stock firmware can't, then certainly DD-WRT or Tomato aftermarket firmwares could. Your Netgear might even be compatible with those firmwares too)