In 2014, the world’s population reached 7.17 billion and was increasing at a rate of 1.1% per year. Assume that this growth rate remains constant. (In fact, the growth rate has decreased since 2008.) 

(a) Write a formula for the world population (in billions) as a function of the number of years since 2014. 

(b) Estimate the population of the world in the year 2020. 

(c) Sketch world population as a function of years since 2014. Use the graph to estimate the doubling time of the population of the world.