A companys total costs and associated output levels for the last four accounting periods have been:

Period	Total costs	Output
1	140,000	8,000 units
2	155,000	11,000 units
3	160,000	12,000 units
4	149,000	9,000 units

What are the estimated fixed costs per period?

Group of answer choices

150,000

120,000

100,000

90,000