The elastic potential energy stored in the spring is
= (1/2) x (spring constant) x (distance stretched or compressed)²
If all four springs are stretched or compressed the SAME distance
from their equilibria, then the potential energy is just proportional
to the spring constant.
From greatest to least stored energy is exactly the same list as
from greatest to least spring constant:
X . . . . . 35
W . . . . . 24
Y . . . . . 22
Z . . . . . 15