**Core Concept**
The positive predictive value (PPV) of a diagnostic test is the proportion of patients with a positive test result who actually have the disease or condition being tested for. In this case, the PPV of ECG for diagnosing myocardial infarction is being calculated.

**Why the Correct Answer is Right**
To calculate the PPV, we need to divide the number of true positives (patients with myocardial infarction and a positive ECG) by the sum of true positives and false positives (patients with a positive ECG). This can be calculated as follows: PPV = (416 / (416 + 9)).

**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect if it was a different calculation, such as PPV = (416 / 520), which would be the sensitivity of the test rather than the PPV.
**Option B:** This option would be incorrect if it was a different formula, such as PPV = (416 / 700), which would be the prevalence of the disease rather than the PPV.

**Clinical Pearl / High-Yield Fact**
When calculating the PPV of a diagnostic test, it's essential to consider the number of false positives, as they can significantly affect the test's accuracy.

**Correct Answer:** B. (416 / (416 + 9)) = 0.979 or 97.9%.