a)
[1, 1, 2] + r·[1, 1, -1] + s·[2, -1, 1] = [1, 4, -1] --> r = 2 ∧ s = -1
[1, 1, 2] + r·[1, 1, -1] + s·[2, -1, 1] = [8, -1, 4] → r = 1 ∧ s = 3
b)
[3, 3, 0] + r·[-3, 3, 2] + s·[0, 0, 1] = [4, 2, 4] --> r = - 1/3 ∧ s = 14/3
[3, 3, 0] + r·[-3, 3, 2] + s·[0, 0, 1] = [0, 7, 3] → keine Lösung