On first picture you see how to transform delta configuration of resistors into star (or Y)
NOTE: If you had ditched R2 you would still get same result of 20Kohm beacuse all resistors are of the same value, but if they were different you would have to use delta to Y transformation
Side question, if picture is worth thousand words, how much is worth picture of words?
Edit: On the second picture where is correctet exponent on 100 should be 100*10^6, not 100*^5