Marlborough Corporation has provided the following for three months of income statements:

January February March

Sales in Units $3,0003,5004,000$

Sales $300,000350,000400,000$

Less: cost of goods sold $120,000140,000160,000$

Gross margin $180,000210,000240,000$

Operating expenses:

Advertising $10,00010,00010,000$

Salaries & Commissions $90,00095,000100,000$

Depreciation expense $25,00025,00025,000$

Utilities expense $7,00019,50022,000$

Total operating expenses $142,000149,500157,000$

Net Income $38,00060,50083,000$

Classify each of the company's expenses as variable, fixed, or mixed.