The average price of regular gasoline in 1997 was $1.26 per gallon. In 2006, the average price of gasoline was $2.31 per gallon. Assume that the average price of gasoline can be modeled by a linear function P (t), where t is the number of years after 1997.
(a) Find a formula for P (t).
(b) Use your answer for part (a) to predict the average price of gasoline in 2020.