Chlorofluorocarbons (CFCs) were used as propellants in spray cans until their buildup in the atmosphere started destroying the ozone, which protects us from ultraviolet rays. Since the 1987 Montreal Protocol (an agreement to curb CFCs), the CFCs in the atmosphere above the US have been reduced from a high of 1915 parts per trillion (ppt) in 2000 to 1640 ppt in 2014.40 The reduction has been approximately linear. Let C(t) be the concentration of CFCs in ppt in year t. (a) Find C(2000) and C(2014). (b) Estimate C ′(2000) and C ′(2014). (c) Assuming C(t) is linear, find a formula for C(t). (d) When is C(t) expected to reach 1500 ppt, the level before CFCs were introduced? (e) If you were told that in the future, C(t) would not be exactly linear, and that C″(t) > 0, would your answer to part 3(d) be too early or too late?