How do you calculate retained earnings?

Problem 3-6A Applying the accounting cycle LO P1, P2, P3, P4, P5 [The following information applies to the questions displayed below. On April 1, 2015, Jiro Nozomi created a new travel agency, Adventure Travel. The following transactions occurred during the company's first month. April 1 Nozomi invested $30,000 cash and computer equipment worth $20,000 in the company in exchange for common stock. 2 The company rented furnished office space by paying $1,800 cash for the first month's (April) rent. 3 The company purchased $1,000 of office supplies for cash. 10 The company paid $2,400 cash for the premium on a 12-month insurance policy. Coverage begins on April 11. 14 The company paid $1,600 cash for two weeks' salaries earned by employees. 24 The company collected $8,000 cash on commissions from airlines on tickets obtained for customers. 28 The company paid $1,600 cash for two weeks' salaries earned by employees. 29 The company paid $350 cash for minor repairs to the company's computer 30 The company paid $750 cash for this month's telephone bill. 30 The company paid $1,500 cash in dividends. The company's chart of accounts follows: 101 Cash 106 Accounts Receivable 124 Office Supplies 128 Prepaid Insurance 167 Computer Equipment 168 Accumulated Depreciation-Computer Equip. 209 Salaries Payable 307 Common Stock 318 Retained Earnings 319 Dividends 405 Commissions Earned 612 Depreciation Expense-Computer Equip. 622 Salaries Expense 637 Insurance Expense 640 Rent Expense 650 Office Supplies Expense 684 Repairs Expense 688 Telephone Expense 901 Income Summary Use the following information in Part 4: a. Two-thirds (or $133) of one month's insurance coverage has expired. b. At the end of the month, $600 of office supplies are still available c. This month's depreciation on the computer equipment is $500. d. Employees earned $420 of unpaid and unrecorded salaries as of month-end. e. The company earned $1,750 of commissions that are not yet billed at month-end