Presented below is the adjusted trial balance of TWK, Inc. at December 31: Debit Credit Cash 10 Accounts Receivable 20 Equipment 200 Accounts Payable 15 Capital Stock 100 Retained Earnings 50 Dividends 5 Service Revenue 180 Salaries Expense 80 Depreciation Expense 20 Supplies Expense 10 Refer to the above data. What is the balance in retained earnings at December 31?