10989 (ie. 98901), 21978 (ie. 87912)
I'll rule out 1xxx2, 2xxx4, 3xxx6, 4xxx8, 1xxx3, 2xxx6, 3xxx9, 1xxx4, 1xxx5, 1xxx6, 1xxx7, 1xxx8 because it's impossible for exact multiples due to the possible quotients and units digits.
That leaves 2xxx8 and 1xxx9. For 1xxx9, it has to be 10xx9 because otherwise if the second digit were 1, it would need to be 11x99 which is clearly impossible. (More than 1 would lead to 6 digits) From here if we create an equation and simplify, we see the fourth digit would be 8. From there we can check 10989 (the only option where multiplying by 9 yields 98xxx), which works.
For the second case:
2abc8 * 4 = 8cba2. a has to be less than 3 so the 10000-s digit of the product is 8. 8cb02 and 8cb22 cannot be multiples of 4, leaving 21bc8*4=8cb12. Again we can write equations, getting c=2 or 7. 21b28 can't work since 21028*4>82000. So, we just need to check b=7,8,9 (again so multiplying by for 21b78 to get 21978 which works.
Sorry if my writing is bad, I'm new.