Find the value of $a$ for which

$v= \displaystyle\left[\begin{array}{c} -3 \cr 6 \cr -5 \cr a \cr \end{array}\right]$

is in the set

$H= span\left\{ \displaystyle\left[\begin{array}{c} -3 \cr 1 \cr -3 \cr 3 \cr \end{array}\right], \displaystyle\left[\begin{array}{c} 0 \cr 5 \cr -3 \cr 2 \cr \end{array}\right], \displaystyle\left[\begin{array}{c} 0 \cr 0 \cr -1 \cr 1 \cr \end{array}\right] \right\}$.

$a=$