hi(Happy)

i have the following system.

x+2y+3z+4t+5u=6

x+3y+5z+7t+4u=13

x+4y+7z+10t+3u=20

x+2y+4z+6t+8u=13

with Gauss method,i ended up here,

x+2y+3z+4t+5u=6

y+2z+3t-u=7

z+2t+3u=7

i don't know how to work with the parameters $\displaystyle t$ and $\displaystyle u$.

thanks.