First of all, you need to define the transfer function: from what point to what point.
In other words, what is the input and what is the output for which you need the transfer function?
I'm solving A=Vout/Vin. I got a answer to the question. I don't need more equations, because there are three nodes and I have three eqs. There are no other nodes to write an equation on. Nor, there is any other relationship which will help.