The data below represent the call volumes over $16$ quarters from a call center at a major financial institution. Develop a forecasting model for the volume of calls $($in $000$ units$).$

$2018201920202021$

Q$1473544628709$

Q$2513582707725$

Q$3582681773854$

Q$4474557592661$

$($a$)$ Develop the quarterly $($Q$1,$ Q$2,$ Q$3,$ Q$4)$ indexes for the volume of calls

See page$117-118$ of text for similar problem

$($b$)$ Create a time series graph showing the: $(1)$ actual data, $(2)$ trend line for the data, and $(3)$ deseasonalized actual data. Label the graph appropriately.

$($c $)$ Using the trend line you developed in Part $($a$),$ what are your seasonally unadjusted and seasonally adjusted forecasts for the four quarters of $2022$ and $2023?$