Solve the system of linear equations $$\left\{ \begin{array}{r@{}r@{}r@{}r} x & + 2 y & -7 z = & -4 \cr 2 x & + y & +z = & 13 \cr 3 x & + 9 y & -36 z = & -33 \end{array} \right.$$ The solutions have the form $x = a + bt , y= c + dt, z= t$, where $t$ is any real number.
Find $a,b,c,d$. $a =$
$b=$
$c =$
$d =$