This looks like an interesting problem. If divides then it also divides and hence it divides . But , and therefore must divide .

But then . Thus , and we only have to investigate the possibilities a = 1, 2 or 3.

When a = 1, the condition that divides becomes: divides , so that must be a factor of 24. You can then check that there are only three such values for b (given that b is different from a). Similar calculations (I'll leave you to work out the details) show that there are no solutions for a=2, and only one solution for a=3.

Spoiler: