How to calculate current through a resistor and LED?
20V supply and 2V across the LED leaves how much voltage across the 3K Ω resistor? 

With that voltage, use ohms law to calculate the current through the 3K Ω resistor.

Calculate the current for a 470 Ω resistor at 2v.
There is more current flowing through the 3K Ω than the 470 Ω resistor.
Where would that excess I3K - I470Ω current go?