How to calculate the carrying amount, I want to know the process.

89. Beynon Corp. purchased office equipment for $20,000, with an estimated residual value of $4,000 at the end of its 8-year useful life. Assuming the double diminishing-balance method is used, the constant percentage to be applied against the carrying amount each year is (a) 10%. (b) 12.5%. (c) 25%. (d) not determinable.