Explanation:
A. The preparation of the closing entries at June 30, 2015 is presented below:
1. Service Revenue A/c Dr $4,300
                 To Income Summary $4,300
(Being revenue account closed)
2. Income summary A/c Dr $3,500
                  To Supplies Expense $1,900
                  To Salaries and Wages Expense $1,344
                  To Miscellaneous Expense $256
(Being expenses accounts are closed)
3. Income summary A/c Dr $800            ($4,300 - $3,500)
                       To Retained earning $800
(Being the difference is credited to retained earning)
4. Retained earnings A/c Dr $628
                          To Dividend A/c $628
(Being dividend account is closed)
2. Now the post-closing trial balance is presented below:
Particulars                                    Debit                           Credit
Cash                                             $3,712
Accounts Receivable                  $3,904
Supplies                                       $480
Accounts Payable                                                             $1,556
Unearned Service Revenue                                             $160
Common Stock                                                                  $4,000
Retained Earnings                                                              $1,932    
Salaries and Wages Payable                                             $448
Total                                              $8,096                           $8,096
The retained earnings is 
= $1,760 + $800 - $628
= $1,932