Consider the data in the table below:

Period

January $$ June July $$ December January $$ June July $$ December January $$ June July $$ December January $$ June July $$ December January $$ June July $$ December

a$.$ Fit a simple linear regression to this period?

Sales $($units$)$

$20104,07520108,23920113,28420116,19420122,58220125,18320131,96820134,02320141,79820143,522$

data. What is your forecast for the January$-$June $2015$b$.$ Now divide the data into two sets: the first half of the year, and the second half of the year. Perform a simple regression on the data for sales in the first half$-$year. What is your forecast for the January$-$June $2015$ period? Do you think this answer is more likely to be accurate than the answer to part $($a$)?$ Why?