3d Geometry

Let L be a line obtained from the intersection of two planes x + 2y + z = 6 and y + 2z = 4. If point P($\alpha$, $\beta$, $\gamma$) is the foot of perpendicular from (3, 2, 1) on L, then the value of 21($\alpha$ + $\beta$ + $\gamma$) equals :