One solution is obviously: (a,b) = (36,36)

Solving for b:

Hence a > 18 and (a - 18) is a factor of 18 or a.

Testing values of a < 36, I found:
(a,b) = (30,45), (27,54), (24,72), (22,99), (21,126), (20,180), (19,342)
and their reversals.