GST return

For GSTR-3B--

If Nil return then 6060+6060=12120

If not nil return then 15150+15150=30300

Figures may differ but deviation will not be much.

For GSTR-1--

Firstly, file all GSTR-3B and then go for GSTR-1. Thus you will get the late fees of GSTR-1 in your next GSTR-3B of Apr 2018.

in gstr 1 we have a max late fee of 5000. is there any max limit of late fee for gstr 3b?

No there is no such limit for 3B. 

my client has paid late fees of rs 1400 from july 2017 to Sept 2017 which has been waived by the department and refunded to him, which was showing in electronic cash ledger...now when iam filing the GSTR-3B For the month of October 2017, iam getting a late fee of 680 Rs.NOW can i use this rs 1400 to pay the latee fee of This 680 rs?

No they have credited it as your tax amount. You will have to pay late fees again by creating a new challan. See your Electronic cash ledger and you will understand.

okay thank you sir.