If for some α and β in R, the intersection of the following three planes x+4 y-2 z=1; x+7 y-5 z=β; x+5 y+α z=5 is a line in R^3, then α+β is equal to:

If for some $\displaystyle \alpha$ and $\displaystyle \beta$ in $\displaystyle \mathbf{R}$, the intersection of the following three planes $$\begin{aligned} & x+4 y-2 z=1 \\ & x+7 y-5 z=\beta \\ & x+5 y+\alpha z=5 \end{aligned} $$ is a line in $\displaystyle \mathrm{R}^3$, then $\displaystyle \alpha+\beta$ is equal to: