Operator decoding and evaluation: Let P denote '÷', Q denote '×', R denote '+' and S denote '−'. Evaluate with standard precedence (×, ÷ before +, −): 18 Q 12 P 4 R 5 S 6

Introduction / Context:
This is a direct operator-decoding exercise. After mapping each code letter to its arithmetic operator, evaluate the expression carefully using standard precedence: perform × and ÷ before + and −, and resolve ties left-to-right.

Given Data / Assumptions:

• P → ÷
• Q → ×
• R → +
• S → −
• Expression: 18 Q 12 P 4 R 5 S 6

Concept / Approach:
Translate first, then compute with precedence, ensuring left-associativity for ×/÷ chains. Do not prematurely add or subtract prior to finishing all multiplications and divisions.

Step-by-Step Solution:
1) Decode → 18 × 12 ÷ 4 + 5 − 6 2) ×/÷ left→right: 18 × 12 = 216; 216 ÷ 4 = 54 3) +/−: 54 + 5 = 59; 59 − 6 = 53

Verification / Alternative check:
Parenthesized: ((18 × 12) ÷ 4) + 5 − 6 = (216 ÷ 4) + 5 − 6 = 54 + 5 − 6 = 53 — consistent.

Why Other Options Are Wrong:
95, 57, and 51 arise from common mistakes such as evaluating +/− too early or reversing left-to-right order in ×/÷.

Common Pitfalls:
Mixing up the code mapping (e.g., treating P as +) or ignoring precedence rules will derail intermediate totals and the final answer.

Final Answer:
53