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 :

Consider the three planes

P₁ : 3x + 15y + 21z = 9,

P₂ : x $$-$$ 3y $$-$$ z = 5, and

P₃ : 2x + 10y + 14z = 5

Then, which one of the following is true?

If (1, 5, 35), (7, 5, 5), (1, $$\lambda$$, 7) and (2$$\lambda$$, 1, 2) are coplanar, then the sum of all possible values of $$\lambda$$ is :

A plane passes through the points A(1, 2, 3), B(2, 3, 1) and C(2, 4, 2). If O is the origin and P is (2, $$-$$1, 1), then the projection of $$\overrightarrow {OP} $$ on this plane is of length :