Conduction - finite difference method

[yecko]

Homework Statement

Homework Equations

Finite difference method

The Attempt at a Solution

I have tried two different approaches, but still i am wrong in the question. Can anyone guide me how to attempt this question?
Thank you

 

[Chestermiller]

The first approach gets the right answer. Why are you saying that it's wrong?

 

[yecko]

The first approach gets the right answer. Why are you saying that it's wrong?

The system says I am wrong (ref: first screenshot in #1), and the following is what my instructor says:
"Are these temperatures computed by you, by solving the finite difference equations ? If these are given in the problem, these are for input data corresponding to the case of delta x = delta y."
I have no clue in understanding how should I do it...
Thank you.

 

[Chestermiller]

Sorry. I have no idea what he's getting at.