Using accumulated depreciation to estimate asset age.

a. Machine A costs $15,000, has accumulated depreciation of $9,000 as of year-end, and is being depreciated on a straight-line basis over 10 years with an estimated salvage value of zero. How long ago was machine A acquired?

b. Machine B has accumulated depreciation (straight-Hne basis) of $8,000 at yearend.
The depreciation charge for the year is $4,000. The estimated salvage value of the machine at the end of its useful life is $2,000. How long ago was machine B acquired?