Flintstone Company amortized a machine that cost $21,600 on a straight-line basis for three years under the assumption it would have a five-year life and a $3,600 trade-in value. At that point, the manager realized that the machine had three years of remaining useful life, after which it would have an estimated $2,160 trade-in value. Determine the amount of amortization to be charged against the machine during each of the remaining years in its life. a. $3,240 b. $1,800 c. $2,640 d. $2,880 e. $3,888