15. Not just the chrome trim on your car, but stainless steel and superalloys also require the metal chromium. In The Limits to Growth in 1972, author Donella H. Meadows and colleagues noted that the world reserves of chromium were 775 million tons, with consumption of 1.85 million tons and consumption growing at 2.6% per year.
15.
(a) 419 years
(b) 96 years