How do you reverse the calculation imposed by a modulus symbol? ie if you encrypt by (number + 7) Mod 10 in an encryption program, how could one write a separate decryption program that accepts an encrypted number and decrypts it back to its original state?

Additionally - how could one code a program that reads in a 1-5 digit integer in a singular textbox then total and print the amount of number 7's typed into the text box?

please help

F

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