Lecturing $/$ academic receipts? $$ My payment summary reflects that I received

$$50,000$ as net salary for my ancillary lecturing services. I can send you a copy of my PAYG Payments Summary where my employer had deducted PAYG of $$20,000.$ I received a payment in my bank account of $$2000$ from a book store for the sale of my text book after tax had been withheld at source of $$400$ which I noted on the book store invoice. The Victorian Law Society also gave me speaker fees of $$3,000$ all up$,$ but no tax was deducted, and I have $2$ invoices recording those fees.

Are you able to please help with the relevant legislative reference from the ITAA $1997$ and the issue regarding this scenario? Is this assessble income?