There is nothing exclusively special about strings and XOR in OTP. We can get the same properties using integers mod n and addition mod n$.$

This problem considers a variant of one$-$time pad, in which the keys, plaintexts, and ci$-$ phertexts are all elements of Zn instead of $\{0,1\}\backslash$lambda $.$

$($a$)$ What is the decryption algorithm that corresponds to the following encryption algo$-$ rithm?