1. The problem asks whether we should substitute values for all terms and the order to evaluate the sum of differences. 2. When evaluating expressions involving sums and differences, substitute the given values for each variable or term first. 3. Then, follow the order of operations: perform all additions and subtractions from left to right. 4. For example, if you have $a - b + c$, substitute values for $a$, $b$, and $c$. 5. Then calculate $a - b$ first, followed by adding $c$ to the result. 6. This ensures the sum of differences is evaluated correctly and consistently. 7. Always substitute all known values before performing arithmetic operations to avoid mistakes.