Suppose an investment of 1,800 doubles in value every 7 years. How much is the investment worth after 42 years?
If the investment doubles in value every 7 years, it means that it doubles 42/7 = 6 times.
Therefore, the investment will be worth 1,800 * 2^6 = 1,800 * 64 = <<1800*64=115200>>115,200 after 42 years. Answer: \boxed{115,200}.