The answers are revealed by subtracting the right side of the equation from both sides.
(a) (2x+3x-6) -(10+4x) = 0
... x -16 = 0 . . . . one solution; neither
(b) (17+5x) -(23+4x-6+x) = 0
... 0 = 0 . . . . . . . an infinite number of solutions; an identity
(c) (7x+4) -(5x+8+2x-10) = 0
... 6 = 0 . . . . . . . no solutions; a contradiction