Bpp question bayle

A part)

How can we come to the conclusion that Fyle will pay employees class 1 Nic @12% and what is *4 ?and also employers class 1 NIC @13.8% *4
How can we come to a conclusion in this way?

B part)

Uber the trading income assessment 2019/2020
Why didn’t we take basis period like 2018/19
and took profit share for period 1.10.19 to 30.09.20 (12 months) how would we know that we have to take 12 months ?
And also Basis period (2nd year-first 12 months of trading)
why there is two sets of dates 1.12.18 to 30.09.19
01.10.19 to 30.11.19

Ii) NiC
Fyle will pay class 2 NIC for 2018/19 of £2.95*18
Could you please tell me what is 18 ?
Is it 18 months

Thank you