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$$\begin{align} (x-1) \;\text{mod}\; 11 &= 3x\; \text{mod}\; 11\\ 11&\lvert(3x-(x-1)) \\ 11&\lvert2x+1\\ x &= 5?\\ \end{align} $$ $$ \begin{align} (a-b)\; \text{mod}\; 5 &= (a+b)\;\text{mod}\;5\\ 5&\lvert a+b-a+b\\ 5&\lvert2b\\ b &= 5/2\\ a &= \text{any integer} \end{align} $$ I don't know how to solve this type of problem. Can you tell me what I have to do generally step-by-step?

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    I edited your question, I hope that I didn't introduce any mistakes.2012-12-07

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