The generator matrix

 1  0  0  1  1  1  1  1  1  1  1  1  1 (a+1)X  0  1  1  1 (a+1)X  1  1
 0  1  0  1  a a+1 (a+1)X (a+1)X+1 (a+1)X+a+1 (a+1)X+a+1 (a+1)X  X (a+1)X  1  1  0 (a+1)X+1  a (a+1)X aX+a  0
 0  0  1 a+1  a  1  1  0  a  0 a+1 (a+1)X+a X+a+1 X+a+1  a X+a (a+1)X+a aX  1 aX+a+1  0
 0  0  0  X  0  X  0 aX (a+1)X  X aX aX  0 (a+1)X  X  X (a+1)X (a+1)X (a+1)X (a+1)X  0
 0  0  0  0  X (a+1)X (a+1)X  0 (a+1)X  X aX  X aX  0  X aX  X (a+1)X  X aX  0

generates a code of length 21 over F4[X,sigma]/(X^2) who´s minimum homogenous weight is 48.

Homogenous weight enumerator: w(x)=1x^0+105x^48+84x^49+48x^51+921x^52+660x^53+240x^54+576x^55+3168x^56+1512x^57+1008x^58+2592x^59+8751x^60+3336x^61+1872x^62+5184x^63+12951x^64+4164x^65+3024x^66+3888x^67+8391x^68+2532x^69+420x^72+81x^76+27x^80

The gray image is a linear code over GF(4) with n=84, k=8 and d=48.
This code was found by Heurico 1.16 in 4.39 seconds.