If the system of linear equations:\( 2x + y - z = 7 \)\( x - 3y + 2z = 1 \)\( x + 4y + \delta z = k \), where \( \delta, k \in \mathbb{R} \)Has infinitely many solutions, then \( \delta + k \) is equal to:
\( -3 \)
\( 3 \)
\( 6 \)
\( 9 \)