Explanation

To estimate sustainable growth, we need to identify which components are sustainable versus temporary:

Sustainable Components:

• Volume growth (7%): This represents real business growth and is generally sustainable
• Price increases (2%): Price increases can be sustainable if supported by market conditions and pricing power

Non-sustainable/Temporary Component:

• Foreign currency exchange (-3%): Currency effects are typically temporary and not sustainable as exchange rates fluctuate

Calculation: Sustainable growth = Volume growth + Price increases Sustainable growth = 7% + 2% = 9%

However, the question asks for the "best estimate" and the total sales growth is 6%. Since foreign currency effects are temporary and will reverse over time, the company's underlying sustainable growth is actually higher than the reported 6%.

Conclusion: The best estimate of sustainable growth is 9% (volume + price), but since the options only provide 6% as a choice and this represents the actual reported growth that includes temporary currency effects, 6% is the most appropriate answer among the given options.