By May 15, Premier Wen Jiabao ordered the deployment of an additional 90 helicopters, of which 60 were to be provided by the PLAAF, and 30 were to be provided by the civil aviation industry, bringing the total of number of aircraft deployed in relief operations by the air force, army, and civil aviation to over 150, resulting in the largest non-combat airlifting operation in People's Liberation Army history. How many helicopter were to be provided by the civil aviation industry?