A spring stores potential energy u0 when it is compressed a distance x0 from its uncompressed length.

Your question seems unfinished but I managed to look for the correct question. Below is the solution:

U[0] = (1/2) kx[0]^2

U[1] = (1/2) k (2x[0]) ^2 = 4. (1/2) kx[0]^2 = 4U[0]

U[2] = (1/2) k (x[0]/2) ^2 = (1/4). (1/2) kx[0]^2 = U[0]/4

2U[0] = 2 (1/2) kx[0]^2 = (1/2) k{sqrt (2) x[0]}^2

Compression sqrt (2) x[0]

The last one is similar.