The Sahara Company Purchased Equipment on January 1, 2015, for $100,000

The Sahara Company purchased equipment on January 1, 2015, for $100,000. The equipment had an estimated residual value of $10,000, an estimated useful life of five years, and estimated lifetime output of 18,000 units. In 2016, the company produced 4,400 units and recorded depreciation expense of $22,000. What depreciation method did the company use?

A) straight-line method
B) sum-of-the-years'-digits method
C) double-declining-balance method
D) units-of-output method