To calculate Stream Tube's market share, we can divide its revenue by the total market revenue and multiply by 100 to express it as a percentage.
Stream Tube's revenue: $15 billion
Total market revenue: $20 billion
Market share = (Stream Tube's revenue / Total market revenue) * 100
Market share = ($15 billion / $20 billion) * 100
Market share ≈ 0.75 * 100
Market share ≈ 75.0%
Therefore, Stream Tube's market share is approximately 75.0%. The correct answer is A. 75.0%.