Let ( p = (x₀, y₀, z₀) ), with ( x₀ > 0 ), ( y₀ > 0 ), and ( z₀ > 0 ), be a point on the surface ( s ) with the equation:
(a) ( x + 2y - 3z = 6 )
(b) ( 2x - y + z = 4 )
(c) ( 3x + y + 2z = 12 )
(d) ( 4x - 3y + 2z = 8 )