The U.S. Centers for Disease Control and Prevention projects that tobacco could soon be the leading cause of death in the world. In 1990, 35 million years of healthy life were lost globally due to tobacco. This quantity was rising linearly at a rate of about 28 million years each decade. In contrast, 100 million years of healthy life were lost due to diarrhea, with the rate falling linearly 22 million years each decade.

(a) Write the years of healthy life in millions lost globally to tobacco as a linear function f_t(t) of the years, t, since 1990.

(b) Write the years of healthy life in millions lost globally to diarrhea as a linear function f_d(t) of the years, t, since 1990.

(c) Using your answers to parts (a) and (b), find in what year the amount of healthy life lost to tobacco was expected to first equal that lost to diarrhea.