How to calculate 35% Tax under Fixed Sum Method (QRMP)?

Quarterly Return Monthly Payment (QRMP) Scheme

Please explain how to calculate 35% Tax to be deposited under Fixed Sum Method?

For example,
A has paid the total tax in qaurter October-December as follows:
CGST = 10000 (9000 ITC + 1000 Cash)
SGST = 10000 (9000 ITC + 1000 Cash)
IGST = 20000 (15000 ITC + 5000 Cash)

(a) 35% should be calculated on total tax liability i.e.
CGST = 35% of 10000 = 3500
SGST = 35% of 10000 = 3500
IGST = 35% 20000 = 7000

Or,
(b) 35% should be calculated on tax paid by cash i.e.
CGST = 35% of 1000 = 350
SGST = 35% of 1000 = 350
IGST = 35% 5000 = 1750

Further, this 35% amount is to be deposited only once in one quarter for example, for January to March Quarter on/before February by 24th.