In each case verify that the following are solutions for all values of s and t.
(a) x = 19t - 35
y = 25 - 13t
z = t
is a solution of
2x + 3y + 2 = 5
5x + 7y - 4z = 0
(b) x1 = 2s + 12t + 13
x2 = s
x3 = - s - 3t - 3
x4 = t
is a solution of
2x1 + 5x2 + 9x3 + 3x4 = -1
x1 + 2x2 + 4x3 = 1