Find all solutions to the following systems.
(a) 3x1 + 8x2 - 3x3 - 14x4 = 2
2x1 + 3x2 - x3 - 2x4 = 1
x1 - 2x2 + x3 + 10x4 = 0
x1 + 5x2 - 2x3 - 12x4 = 1
(b) x1 - x2 + x3 - x4 = 0
-x1 + x2 + x3 + x4 = 0
x3 + x2 - x3 + x4 = 0
x1 + x2 + x3 + x4 = 0
(c) x1 - x2 + x3 - 2x4 = 1
-x1 + x2 + x3 + x4 = -1
-x1 + 2x2 + 3x3 - x4 = 2
x1 - x2 + 2x3 + x4 = 1
(d) x1 + x2 + 2x3 - x4 = 4
3x2 - x3 + 4x4 = 2
x1 + 2x2 - 3x3 + 5x4 = 0
x1 + x2 - 5x3 + 6x4 = -3