Question 183774
There's a whole alphabet to choose from.  There's a Greek alphabet, too, but it has only 24 letters.
---------------
Anyway, I think what you want here is a relationship between the 2 sets of numbers.
Start with the biggest pair, 15 and 72.  To get 72 from 15, you can multiply by 4 and add 12.  That doesn't work for the others, tho.
If you muliply by 5 and subtract 3...
Try that one.
------------
k = 5m - 3
You already had the letters.