There's a typo in the table shown. In City's case it says Purchased Gross £46 million. Remembering Mendy, Zayette, etc, I think it should say Purchased Dross.
I suspect they look at the accounts, if you spent the time I'm pretty sure you could work out the fees using the additions/disposals and amortisation figures alongside the publicly known facts/figures.
We need to get more in that sold column. I don't see a lot of decent profit in what we have. WE need to be signing players with the aim of selling them on in 2 seasons time