The generator matrix

 1  1  1  1  1  1  1  1  X  X  X  0  0  0  X  1  1  1
 0  X  0  X  0  0  X  X  0  X  X  X  X  0  0  0  0  X
 0  0  X  X  0  X  X  0  X  X  0  0  X  X  0  0  X  X

generates a code of length 18 over Z2[X]/(X^2) who´s minimum homogenous weight is 18.

Homogenous weight enumerator: w(x)=1x^0+3x^18+8x^19+3x^20+1x^22

The gray image is a linear code over GF(2) with n=36, k=4 and d=18.
As d=18 is an upper bound for linear (36,4,2)-codes, this code is optimal over Z2[X]/(X^2) for dimension 4.
This code was found by Heurico 1.16 in 0.000693 seconds.