Final answer:
To calculate depreciation expense using the modified half-month convention for the year ending December 31, 2018, subtract the residual value from the cost of the equipment and then divide it by the estimated useful life in months. Multiply this monthly depreciation expense by the number of months the asset is available for use in the first year to get the depreciation expense for the year.
Step-by-step explanation:
To calculate depreciation expense using the modified half-month convention, you need to determine the number of months that the asset is available for use in the first year. In this case, the equipment was acquired on March 17, 2018, so it is available for use for 9 and a half months in 2018 (from March 17 to December 31).
Next, you need to calculate the monthly depreciation expense by subtracting the residual value from the cost of the equipment and then dividing it by the estimated useful life in months. The monthly depreciation expense is ($140,000 - $42,000) / (8 x 12) = $825.
Finally, you can calculate the depreciation expense for the year ending December 31, 2018 by multiplying the monthly depreciation expense ($825) by the number of months the asset is available for use in the first year (9.5 months). The depreciation expense for the year ending December 31, 2018 is $7,837.50.