On July 1, 20X1, ZipCo, which uses UOP depreciation, purchases a truck for $36,000 with an estimated useful life of 100,000 miles and a residual value of $6,000. Miles driven are as follows: Year Miles 20X1 5,000 20X2 10,000 20X3 20,000 20X4 25,000 20X5 30,000 The depreciation expense for 20X6: cannot be determined with the given data $900 $750 $3,600 $3,000