The generator matrix

 1  0  0  1  1  1  X  1  1  1  1  1  1  1  1  1  1  1  1  0  X
 0  1  0  X  1 X+1  1  X  0  0  1 X+1 X+1  X  1  0  X X+1  1  1  1
 0  0  1  1 X+1  X  1 X+1  1  X  1  0 X+1  0  X X+1  X  1  0  X  X

generates a code of length 21 over Z2[X]/(X^2) who´s minimum homogenous weight is 20.

Homogenous weight enumerator: w(x)=1x^0+32x^20+24x^22+6x^24+1x^32

The gray image is a linear code over GF(2) with n=42, k=6 and d=20.
As d=20 is an upper bound for linear (42,6,2)-codes, this code is optimal over Z2[X]/(X^2) for dimension 6.
This code was found by Heurico 1.16 in 0.00142 seconds.