Read this and answer the question. If the question is unanswerable, say "unanswerable".

As of 2007, the total installed capacity of solar hot water systems is approximately 154 thermal gigawatt (GWth). China is the world leader in their deployment with 70 GWth installed as of 2006 and a long-term goal of 210 GWth by 2020. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GWth as of 2005.

What was the total capacity of solar hot water systems in 2007 in gigawatts?
154