Only want help with part c. Double diminishing balance

S6-5 Assume that at the beginning of 2020, Porter Airlines purchased a Bombardier Q400 aircraft at a cost of $25,000,000. Porter expects the plane to remain useful for five years (5,000,000km) and to have a residual value of $5,000,000. Porter expects the plane to be flown 750,000km the first year and 1,250,000 km each year during years 2 through 4, and 500,000km the last year. S6-6 Use the assumed Porter Airlines data in exercise S6-5 to compute Porter's fifth-year depreciation on the plane using the following methods: a. Straight-line b. Units-of-production c. Double-diminishing-balance Learning Objective 2 Compute depreciation by three methods-final year only