\begin{align} x-\hphantom{2}y+2z+2t&=0 \\ 2x-2y+4z+3t&=1 \\ 3x-3y+6z+9t&=-3 \\ 4x-4y+8z+8t&=0 \end{align}
Solve for x,y,z and t

\begin{align} x-\hphantom{2}y+2z+2t&=0 \\ 2x-2y+4z+3t&=1 \\ 3x-3y+6z+9t&=-3 \\ 4x-4y+8z+8t&=0 \end{align}
Solve for x,y,z and t

Then treat any two variables as constants and express other two in terms of those constants
For Example if you keep $x$ and $y$ as constants then $$z=\frac{y-x+2}{2}$$ $$t=-1$$