Final answer:
The journal entry that Robertson makes on October is Cash 3,920, Sales Discounts 80, Accounts Receivable 4,000. Therefore, the correct option is C.
Step-by-step explanation:
The correct journal entry that Robertson makes on October is:
C. Cash 3,920
Sales Discounts 80
Accounts Receivable 4,000
When Alberts pays the invoice on October 8 and takes the appropriate discount, Robertson will record the cash received along with the sales discounts granted. The cash amount will be $3,920 because the customer took advantage of the discount, and the remaining amount ($4,000) will be recorded as a reduction in the accounts receivable balance.