1. The problem asks to find the sum or difference of given values and then determine the corresponding letter using a decoder. 2. To solve sum or difference problems, use the formula: $$\text{Result} = a \pm b$$ where $a$ and $b$ are numbers. 3. Important rules: - When adding, combine the values directly. - When subtracting, subtract the second value from the first. 4. Perform each sum or difference step by step, showing intermediate work. 5. After finding the numerical result, use the decoder to find the corresponding letter. Since no specific numbers or decoder were provided, please provide the values and decoder for a complete solution.