The generator matrix

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

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+144x^48+96x^49+264x^50+972x^51+1842x^52+1644x^53+2052x^54+4380x^55+8154x^56+5472x^57+6336x^58+14376x^59+24591x^60+15384x^61+15576x^62+30312x^63+39570x^64+19488x^65+15576x^66+21324x^67+21078x^68+7068x^69+3204x^70+2364x^71+792x^72+51x^76+27x^80+6x^84

The gray image is a linear code over GF(4) with n=84, k=9 and d=48.
This code was found by Heurico 1.16 in 51.5 seconds.