In each of the follow ing, find conditions on a and b such that the system has no solution, one solution, and infinitely many solutions.
(a) x - 2y = 1
ax + by = 5
(b) x + by = -1
ax + 2y = 5
(c) x - by = -1
x + ay = 3
(d) ax + y = 1
2x + y = b