If A, B, C, D,.........Z represents numbers from 1, 2, 3,...... 26. Key can be anything from 1 to 25. For a key of 2, every letter shifts 2 places. To right A becomes C, Z becomes B and so on. If key is equal to 9, match the normal letters with encrypted letters.
Normal LetterEncrypted Letter1 Aa Y2 Fb D3 Pc O4 Ud I5 Ze J
1e, 2c, 3a, 4b, 5d
Since key = 9, we have to shift letters 9 places to the right.
"Given positionKeyEncrypted letter at positionEncrypted letterA−1910JF−6915OP−16925YU−21930−26=4DZ−26935−26=9I"