Answer and Explanation:
The Journal entry is shown below:-
1. Cash Account Dr, $10,400 Â
        To Sales account $10,000
        To Sales Tax Payable account $400    ($10,000 × 4%)
(Being cash received is recorded)
Here we debited the cash as it increased the assets and we credited the sales and sales tax payable as it increased the sales and liabilities.
2. Cost of Goods Sold Dr, $5,000 Â
         To Inventory $5,000
(Being Cost of Goods sold is recorded)
Here we debited the cost of goods sold as it increase the expenses and we credited the inventory as it decrease the assets
3. Unearned Services Revenue Dr, $50,000 Â
         To Earned Services Revenue  $50,000
(Being unearned service revenue is recorded)
Here we debited the unearned service revenue as it decreased the liabilities and we credited the earned service revenue as it increased the sales