Matrices and Determinants: JEE Main 2021 Mathematics question

For real numbers $\alpha$ and $\beta$, consider the following system of linear equations : x + y $-$ z = 2, x + 2y + $\alpha$z = 1, 2x $-$ y + z = $\beta$. If the system has infinite solutions, then $\alpha$ + $\beta$ is equal to ______________.