flat rate expense

I am not quite clear on flat rate expense of private use of part of a commercial building.
In the book it is described as ”private use adjustment are household goods and services, rent,food,and utilities=fixed amount based on number of occupants. so what does this mean?

In 1 question, it is asked to calculate adjusted trading profit according to cash basis.

”the cash basis private use adjustment for two occupants in a business premises for 8 months is 4000”
this was added when calculating adjusted trading profit. but why?

in other question it was, ”the cash basis private use adjustment for one occupant in a business premises for 12 month period is 4200”. but, here no value was added or subtracted .