The average monthly price of regular gasoline in Southern California is monitored by the Automobile Club of South-ern California’s monthly Fuel Gauge Report. The prices of the time period July 2004 to June 2006 are given here.

a. Produce a time-series plot of the average price of regular gas in Southern California. Identify any time-series components that exist in the data.
b. Identify the recurrence period of the time series. Determine the seasonal index for each month within the recurrence period.
c. Fit a linear trend model to the deseasonalized data.
d. Provide a seasonally adjusted forecast using the linear trend model for July 2006 and July 2010.