Well, you've stated that Ron = L/W so all calculations are simply those used for resistors.
There are two current paths to ground from Y. One through A & B, and the other through C & D & B. The worst case resistance to ground is when only one of these current paths are conducting.
If both current paths are conducting, then the resistance to ground will be reduced and is obviously not worst case.
You simply have to find some values for L/W that allow the total resistance from Y to ground to be 1/2.22 (assuming as you wrote Ron = L/W).
Referring to the left diagram, if the path A&B is formed, the resistance from Y to ground is Rab = 1/3.33 + 1/6.66 = 0.45... the W/L value is 1/0.45 = 2.22, which is what was asked for.
If path C&D&B is formed, the W/L from Y to ground is 1/Rcdb = 1/(1/6.66 + 1/6.66 + 1/6.66) = 2.22, which is also the value you're after.
The same goes for the values in the figure to the right. 1/(1/4.44 + 1/4.44) = 2.22 = 1/(1/8.88 + 1/8.88 + 1/4.44) = 2.22