Find the point of intersection (if any) of the following

Find the point of intersection (if any) of the following pairs of lines.
(a) x = 1 - t x = 2s
y = 2 + 2t y = 1 + s
z = -1 + 3t 2 = 3
(b) [x y z]T = [4 -1 5]T + t[1 0 1]T
[x y z]T = [2 -7 12]T + s[0 -2 3]T