Answer:
Windsor Solar Panels, Inc.
Date        Account Titles and Explanation             Debit       Credit
July 1       Accounts Receivable (Wildhorse Co.) $128,000
               Sales Revenue                                                  $128,000
To record the sale of solar panels, terms 3/15, n/30.
July 12    Accounts Receivable (Novak Corp.)     $82,000
               Sales Revenue                                                   $82,000
To record the sale of solar panels, terms  4/10, n/60.
July 18   Cash Account                                       $78,720
              Cash Discount                                        $3,280
              Accounts Receivable (Novak Corp.)                 $82,000
To record the receipt of payment from Novak Corp.
July 20 Sales Allowances                                   $2,100
             Accounts Receivable (Wildhorse Co.)                $2,100
To record the credit allowance granted to Wildhorse Company.
July 29 Cash Account                                     $125,900
             Accounts Receivable (Wildhorse Co.)                $125,900
To record the receipt of payment from Wildhorse Company
July 31  "No Entry"
Explanation:
Windsor Solar Panels, Inc. will record the above journal entries to initially record the business transactions that take place within the period.  These journal entries determine the accounts to be debited and the ones to be credited in the general journal.