E$14-24.$ Selecting a Basis for Predicting Shipping Expenses $($Requires Computer Spreadsheet$*)$ Cambridge SoundWorks sell portable speakers systems and bluetooth headphones. In an effort to improve the planning and control of shipping expenses, management is trying to determine which of three variables$-$units shipped, weight shipped, or sales value of units shipped$-$has the closest relationship with shipping expenses. The following information is available:

$\backslash$table$[[$Month$,\backslash$table$[[$Units$],[$Shipped$]],\backslash$table$[[$Weight$],[$Shipped $($Ibs$.)]],\backslash$table$[[$Sales Value of$],[$Units Shipped$]],\backslash$table$[[$Shipping$],[$Expenses$]]],[$May$.,10,000,7,500,$$$350,000,$$$38,000],[$June$,12,000,8,760,432,000,42,000],[$July$.,15,000,9,200,420,000,50,100],[$August$,20,000,10,500,400,000,72,500],[$September$,12,000,7,600,300,000,41,000],[$October$......,8,000,6,000,320,000,35,600]]$

REQUIRED

a$.$ With the aid of a spreadsheet program, determine whether units shipped, weight shipped, or sales value of units shipped has the closest relationship with shipping expenses.

b$.$ Using the independent variable that appears to have the closest relationship to shipping expenses, develop a cost$-$estimating equation for total monthly shipping expenses.

c$.$ Use the equation developed in requirement $(b)$ to predict total shipping expenses in a month when $14,000$ units, weighing $9,380lbs.,$ with a total sales value of $$420,000$ are shipped.