- This is a standard arithmetic math(s) problem where each number has been uniquely replaced by a symbol.

- Each symbol stands for a distinct number that, when filled in, will complete the equation correctly.

- - (e.g. "N + N + N = YN", you can deduce N = 5 and Y = 1, as they're the only numbers that fit.)

- Once you have the correct numbers, fill them out from left to right in the code entry.

- Figure out "backwards N" number first.

-This tells you that several symbols stand for 1, 2, and 3.

"backwards N" = 1

You know this because, in arithmetic, the only carried number when two numbers are added can be a 1. Even 999 + 999 is still 1,998.