In this circuit... how come you just ignore the 6.8 k resistor, and the two 10k to find the voltage at the 2.2 to then get the current across the diode...
do not the 6.8 k resistor, and the two 10k have an effect on the circuit?
Since the resistors are connected in parallel to the voltage source, they do not affect the rest of the circuit voltage-wise (unless of course their resistances are set to 0).
Well, you started by asking about voltage (correctly, since for this you need v=ir), but ask yourself this: does current going through the diode also go through those resistors?
You can also think of it this way. If you remove the diode from the circuit, you will have two terminals, A and B (across the 2.2K resistor). The voltage that the diode or any component will see when connected to these terminals will be the voltage drop across the 2.2K resistor. You can find the voltage drop across that resistor by using the voltage divider formula. And from here, you can go ahead to find the current.
