You need to first understand the basic motive behind section 44AD here the government is putting trust over small business and saving them from the burden of maintaining books against this they only ask the businesses to show 8% or actual profit whichever is higher.
Businesses have to provide 4 figures to the government and for that one don't need to maintain books, every person managing a business knows what profit he is earning even without maintaining books.
If you don't have any explanation for your expense then income tax can even assume all credit entries in your bank account as your income.
Now to answer your second question one need to show 8.5% profit as section 44AD says 44AD considers all profit after taking into consideration all PGBP provisions therefore one will show 8.5% profit.
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