Consider the system of linear equations $$ \begin{aligned} & -x+y+2 z=0 \\ & 3 x-a y+5 z=1 \\ & 2 x-2 y-a z=7 \end{aligned} $$ Let $S_1$ be the set of all $a \in R$ for which the system is inconsistent and $S_2$ be the set of all $a \in R$ for which the system has infinitely many solutions. If $n\left(S_1\right)$ and $n\left(S_2\right)$ denote the number of elements in $S_1$ and $S_2$ respectively, then