World grain production was 1241 million tons in 1975 and 2048 million tons in 2005, and has been increasing at an approximately constant rate.

(a) Find a linear function for world grain production, P, in million tons, as a function of t, the number of years since 1975. 

(b) Using units, interpret the slope in terms of grain production. 

(c) Using units, interpret the vertical intercept in terms of grain production. 

(d) According to the linear model, what is the predicted world grain production in 2015? 

(e) According to the linear model, when is grain production predicted to reach 2500 million tons?