New car sales for a dealer in Cook County, Illinois, for the past year are shown in the following table, along with monthly indexes $($seasonal relatives$),$ which are supplied to the dealer by the regional distributor.

$\backslash$table$[[$Month$,$Units Sold,Index$],[$Jan$.,640,0\mathrm{.}80],[$Feb$.,648,0\mathrm{.}80],[$Mar$.,630,0\mathrm{.}70],[$Apr$.,761,0\mathrm{.}94],[$May$.,735,0\mathrm{.}89],[$Jun$.,850,1\mathrm{.}00],[$Jul$.,765,0\mathrm{.}90],[$Aug$.,805,1\mathrm{.}15],[$Sept$.,840,1\mathrm{.}20],[$Oct$.,828,1\mathrm{.}20],[$Nov$.,840,1\mathrm{.}25],[$Dec$.,800,1\mathrm{.}25]]$

a$.$ Plot the data. Does there seem to be a trend?

b$.$ Deseasonalize car sales.

c$.$ Plot the deseasonalized data on the same graph as the original data. Comment on the two graphs.

d$.$ Assuming no proactive approach on the part of management, discuss $($no calculations necessary$)$ how you would forecast sales for the first three months of the next year.