Interchange operations and digits: After swapping “+” with “−” and the digits 8 with 7 everywhere, which equality becomes correct?

Introduction / Context:
This puzzle requires two simultaneous substitutions: exchange “+” with “−” and swap every 8 with 7 (and vice versa). After that, we test the equalities.

Given Data / Assumptions:

• Swaps apply globally and consistently.
• “x” is ordinary multiplication.

Concept / Approach:
Perform symbol and digit swaps carefully, then evaluate LHS and compare with RHS.

Step-by-Step Solution:
(C) Original: 6 + 8 x 2 - 7 = 0. Swap 8↔7 → 6 + 7 x 2 - 8; swap +↔− → 6 − 7 x 2 + 8. Compute: 7 x 2 = 14; 6 − 14 + 8 = 0. Equality holds. Other options, after both swaps, do not evaluate to the stated RHS.

Verification / Alternative check:
Recalculate by writing the transformed expression explicitly and applying precedence (× before ±).

Why Other Options Are Wrong:
After the double swap, their LHS numeric values differ from their RHS, so they are false equalities.

Common Pitfalls:
Forgetting to swap every occurrence or mixing the order of swaps. Because swapping is symmetric, order does not matter, but consistency does.

Final Answer:
6 + 8 x 2 - 7 = 0