Respuesta :

The pattern seems to be to reverse the number order, add two, then repeat.
34 flipped to 43, so the next step would be to add two--45. 
bookishfairy73
12, 21, 23, 32, 34, 43,45because 12 flips to 21
23 flips to 32
34 flips to 43
and 45 would flip to 54 i picked this because 12 is 1 and 2 so 23 is 2 and 3 and 34 is 3 and 4 so 45 is 4 and 5