Toowoomba solar limited wants to find an equation to estimate some of their monthly operating costs for the coming year. The following cost and other data were gathered for the previous 12 months:

Month	Maintenance	Machine-hours	Health insurance	Number of employees	Shipping costs	Units shipped
January	2250	1656	4300	68	12888	1432
February	2226	120	4300	75	14832	1648
March	2300	230	4300	92	14337	1593
April	2425	318	4300	105	11529	1281
May	2583	460	4300	89	10647	1183
June	2380	280	4300	87	16641	1849
July	2455	340	4300	93	15714	1746
August	2480	360	4300	88	15147	1683
September	2535	420	4300	95	12555	1395
October	2625	495	4300	102	12933	1437
November	2655	510	4300	97	10062	1118
December	2380	275	4300	94	17298	1922

1. Which of the above costs is variable? Fixed? Mixed? Explain.
2. Using the high-low method, determine the cost function for mixed cost.
3. Combine the information above to get a monthly utility cost function for TSL.
4. Next month, TSL expects to use 400 machine-hours, have 80employees and ship 2000 units. Estimate total operating cost for the month.