Annual revenue R from McDonald’s restaurants worldwide between 2013 and 2015 can be estimated by R = 28.1 − 1.35t, where R is in billion dollars and t is in years since January 1, 2013. 

(a) What is the slope of this function? Include units. Interpret the slope in terms of McDonald’s revenue. 

(b) What is the vertical intercept of this function? Include units. Interpret the vertical intercept in terms of McDonald’s revenue. 

(c) What annual revenue does the function predict for 2018? 

(d) If revenue continues to decline at the same rate, when is annual revenue predicted to fall to 22 billion dollars?