What is the annual percentage rate of interest on terms: 3/7, net 27?

WHAT WOULD BE THE EASIEST WAY TO CALCULATE THIS ON A CALCULATOR?

 

Balance Sheet Assets Cash 2013 Income Statement 2013 Sales $ 650,000 $ 270,000 Cost of Goods Sold 182,000 Accounts Receivable 113,400 Gross Profit $ 468,000 Inventory Prepaid Expenses Total Current Assets Fixed Assets 86,400 Interest Income 65,000 13,500 Total Income $ 533,000 $ 483,300 Sales Salaries 149,500 32,400 Office Salaries 32,500 Total Assets $ 515,700 Office Equipment Rental 45,500 Liabilities & Equity Interest Expense 19,500 Accounts Payable $ 87,669 General & Administrative 5,850 Notes Payable Accrued Expenses Taxes Payable 46,413 Total Expenses $ 252,850 41,256 Income Before Tax 280,150 36,099 Income Taxes 162,500 Deferred Taxes 46,413 Net Income $ 117,650 Total Current Liabilities $ 257,850 Long-Term Notes 118,611 Total Liabilities Capital Stock Retained Earnings Total Equity Total Liabilities & Equity $ 376,461 51,570 87,669 $ 139,239 $ 515,700