Hello, For Chapter 4, Problem 8P how was the "Net Income" of $18,000 calculated? Thank you,

OS Clinic Income Statement For year ended December 31, 2015 Net patient service revenue $35,000 Total revenue 35,000 Expense: Supplies expense 7,000 Depreciation expense 10,000 Total expense 17,000 Net income 18.000 Notes: The net patient revenue will be the total collection in cash and credit. The cash collection will be $25,000 (difference between the cash balances of two years). The credit collection will be $10,000 (difference between the accounts receivable balances of two years). The supplies expense will be the difference between the liabilities for two years. It will be the accounts payable for supplies. The depreciation expense for this year will be difference between the net properties for two years. The difference in property will be due to the depreciation as there is no sale or purchase