I tried calculating the current flowing through the diodes using:

v2-v1 = 2.3nVt log (I2/I1)

solving for I2

Since IL = 0,

then the current flowing through the resistor should be I2 which I calculated to be 3.16mA

The voltage across is 15V - 3V = 12V

However the final resistance is 12/3.16mA = 3.79 K ohms

The answer given is 4.8K ohms.

Can someone pls help me understand what I am doing wrong?

And just a quick question, would it be right to equate saturation current Is with the junction area since they are proportional.

Thank you so much for your help