Prepare general journal entries on December 31, 2015 to record the following unrelated year-end adjustments. (a) On December 2, 2015, $6,200 of supplies were purchased and recorded as an asset. A count revealed $1,000 still on hand at December 31, 2015. (b) Services performed during December but not yet billed to customers totalled $5,000. (c) Depreciation of equipment is recorded using the straight-line method over 10 years. The equipment was purchased on December 1, 2015 for $300,000, and has no residual value at the end of its useful life. (d) Prepaid insurance expired during the month of December was $2,500.