Mine was the following :
I noticed that for AB to BA the difference grows by a factor of nine that goes * X for each + 1 increment to B and that said factor goes one step forwards when A goes one digit up, like such :
23 to 32 is 9
24 to 42 is 18
34 to 43 is 9
35 to 53 is 18.
I know that I must add 90 to AB to get AoB
Since speed is constant you must add 45 to AB and BA. and since 9*5= 45 you've got to take the fifth rank as from AB ( for 23 you go 4 up as the first rank is included in the first AB (23) hence 27 to 72 is indeed 45 ).
Hence AB + 90 = AoB, 4
5+ A = B
Then I tried with 27 to 72 which is 45, 5+2(A) = 7 = B but 4+ 7(B) = 11 and it has to produce a 10, if B continues going 1 up 4 + B will take + 1 each time.
Ok but what if you get 4 + B = 20 or 30 or 40 ?
If A goes + 1 it gives you 38 to 83 and 5 + 3 = 8 ( ok here but as said above 4 + B will equal 12 ), 49 to 94 = 45 but 5 + 4 = 9 and 5 + A cannot equals B.
So as you cannot add + 1 to either A or B and as it does not work as from 27 to 72 the only solution left is A = 1 and B = 6. A goes 1 down and as you have to respect the 'rank" thing it has to be 12 + 4 "ranks" up = 16.
And it worked ! !!!
I told you it was way too complicated
@ abcxyz
I still don't understand where the second line of your equation comes from, though.