Equipment costing $130,000 is expected to have a residual value of $10,000 at the end of its six year useful life. The equipment is metered so that the number of units processed is counted. The equipment is designed to process 1,000,000 units in its lifetime. In 2019 and 2020, the equipment processed 180,000 units and 140,000 units respectively. Calculate the depreciation expense for 2019 and 2020 using each of the following methods:

a. Straight-line

b. Double-declining-balance

c. Units of production