Query about question "$x$ is an odd integer..." [1431]

https://www.gregmat.com/problems/quant?problem=x-is-an-odd-integer

Hi I plugged in 3 for the equation for my odd integer, I get a value of 4 and 3 when solving for the equations. I am a bit confused why the solution is 0. Can someone help explain why my brain cannot wrap itself around this concept? Ty

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