Use the computer to solve these systems from the second subsection.
(a) 3x + 6y = 18
x + 2y = 6
(b) x + y = 1
x - y = -1
(c) x1 + x3 = 4
x1 - x2 + 2x3 = 5
4x1 - x2 + 5x3 = 17
(d) 2a + b - c = 2
2a + c = 3
a - b = 0
(e) x + 2y - z = 3
2x + y + w = 4
x - y + z + w = 1
(f) x + z + w = 4
2x + y - w = 2
3x + y + z = 7