Statement (A): $3+14$  is a mathematical statement.

Statement (B): $3x-y+z=9$ is a mathematical statement.

I) $3+14$  is a numerical expression.

II)$3x-y+z=9$

For  $x=2,y=0,z=3$ , above statement is true.

$x=1,y=0,z=3$ , above statement  is false.

So given statement we can’t say either true or false.

$\therefore$  it is not a  mathematical statement