Spoiler!
subtract and all this other. S is the 19th letter...A is the 1st....19-1=18 not 17! Stop saying look for the pattern or trying to be cute...if you click on the spoiler tag...help folks!
Without outright giving the answer, don't do simple subtraction of number value.
Count instead the number of characters between the two letters. Give yourself 2 number lines. A -> Z and Z -> A. In the standard count positive difference between two word characters you've assigned. In reverse, count negative (example of the letter above is D and the letter below is B, use this one). Thus the number of characters between A and S is 17 characters.
Without outright giving the answer, don't do simple subtraction of number value.
Count instead the number of characters between the two letters. Give yourself 2 number lines. A -> Z and Z -> A. In the standard count positive difference between two word characters you've assigned. In reverse, count negative (example of the letter above is D and the letter below is B, use this one). Thus the number of characters between A and S is 17 characters.