I'm confused on the "Depreciable Units" part. I'm not sure what I'm supposed to do. Year 4's Depreciation expense I know is different too

A machine costing $211,600 with a four-year life and an estimated $18,000 salvage value is installed in Luther Company's factory on January 1. The factory manager estimates the machine will produce 484,000 units of product during its life. It actually produces the following units: 123,000 in Year 1, 122,800 in Year 2,120,400 in Year 3,127,800 in Year 4. The total number of units produced by the end of Year 4 exceeds the original estimate-this difference was not predicted. Note: The machine cannot be depreciated below its estimated salvage value. Required: Compute depreciation for each year (and total depreciation of all years combined) for the machine under each depreciation method. Note: Round your per unit depreciation to 2 decimal places. Round your answers to the nearest whole dollar. Complete this question by entering your answers in the tabs below. Compute depreciation for each year (and total depreciation of all. years combined) for the machine under the Units of production