Electric Dreams Corporation is a wholesaler of a large variety of light fittings and other lighting needs. The company's accountant, Henry Benry, has recently completed a cost study of the firm's shipping department in which he used the weight of supplies loaded or unloaded at the company's loading dock to quantify the department$$s activity. Henry compiled the following data.

Month

Supplies loaded or unloaded $($kg$)$

Shipping department costs

January

$5,400$ $$70,200$

February

$4,80067,800$

March

$3,90067,500$

April

$3,00061,200$

May

$6,60066,600$

June

$7,20075,300$

July

$6,00072,000$

August

$5,40068,400$

September

$7,80072,720$

October

$3,30066,300$

November

$3,60068,100$

December

$4,20068,100$

Required:

a$.$ Estimate the shipping department's cost behaviour using the high low method. Use an equation to express the results of this estimation method.

b$.$ Predict the shipping department$$s cost for a month when loads totalling $4,500$ kilograms are moved.