Computation of Depreciation Expense

Feng Company purchased a machine for $180,000 on September 1, 2013. It is estimated that the machine will have a 10-year life and a salvage value of $18,000. Its working hours and production in units are estimated at 36,000 and 750,000, respectively. It is the company's policy to depreciate assets for the number of months they are held during a year. During 2013, the machine was operated 1,500 hours and produced 21,000 units.

Calculate depreciation expense for all four methods. Do not round interim calculations. Round your final answers to the nearest dollar.

Double-declining-balance depreciation: = $12000

Sum-of-the-years'-digits depreciation: = ?

Productive-output depreciation: = ?

Service-hours depreciation: = $6750

Select the method that will give the greatest depreciation expense for 2013.

Double-declining-balance

I have got 3/5 of the answers. I still need Sum of the Year and productive out put. Please show your work. Thank you.