Forecasting airline interest in larger-capacity models, Boeing announced the stretched 767-300 in 1983 and the extended-range 767-300ER in 1984. Both models offered a 20 percent passenger capacity increase, while the extended-range version was capable of operating flights up to . Japan Airlines placed the first order for the 767-300 in September 1983. Following its first flight on January 30, 1986, the type entered service with Japan Airlines on October 20, 1986. The 767-300ER completed its first flight on December 9, 1986, but it was not until March 1987 that the first firm order, from American Airlines, was placed. The type entered service with American Airlines on March 3, 1988. The 767-300 and 767-300ER gained popularity after entering service, and came to account for approximately two-thirds of all 767s sold.
Question: How many months after the first flight of the 767-300 was the first flight of the 767-300ER?
Answer: 12