Write a question about the following article: Sydney has been a manufacturing city since the protectionist policies of the 1920s. By 1961 the industry accounted for 39% of all employment and by 1970 over 30% of all Australian manufacturing jobs were in Sydney. Its status has declined in more recent decades, making up 12.6% of employment in 2001 and 8.5% in 2011. Between 1970 and 1985 there was a loss of 180,000 manufacturing jobs. The city is still the largest manufacturing centre in Australia. Its manufacturing output of $21.7 billion in 2013 was greater than that of Melbourne with $18.9 billion. Observers have noted Sydneys focus on the domestic market and high-tech manufacturing as reasons for its resilience against the high Australian dollar of the early 2010s.
How many billions of dollars did Sydney and Melbourne combine output in manufacturing in 2013?