Let $A$ be a square matrix of order $3$ whose all entries are $1$ and let $I_3$ be the identity matrix of order $3.$ Then, the matrix $A-3I_3$ is

The system of equations

$\lambda x+y+3z=0$

$2x+\mu y-z=0$

$5x+7y+z=0$

has infinitely many solutions in $R.$ Then,

If the following three linear equations have a non-trivial solution, then

$x+4ay+az=0$
$x+3by+bz=0$
$x+2cy+cz=0$