please provide all calculations in detail with answers

The following information pertains to Seven Dwarf Mining Equipment Limited for 2019 and 2020: Cost of Operating Number of the Purchasing Purchase Degartment Qrders Issued Fourth quarter of 201i;I $130,000 2,500 First quarter of 2020 30,000 1,000 Second quarter of 2020 110,000 1,500 Third quarter of 2020 115,000 2,000 Fourth quarter of 2020 140,000 3,000 Required: Using the high-low method, determine the following: a. The variable cost per purchase order. b. The fixed cost of operating the purchasing department for one quarter. c. The estimated cost of operating the purchasing department in first quarter of 2021 assuming that 2,800 purchase orders will be issued