I have the correct answers for numbers 2,8, and 9 but I dont understand why the answer is what it is.

EX 1-12 Transactions The following selected transact February: OBJ. 4 ions were completed by Silverado Delivery Service during 1. Received cash from owner as additional investment, $25,000. 2. Purchased supplies for cash, $750. 3. Paid rent for February, $3,000. 4. Paid advertising expense, $1,500 5. Received cash for providing delivery services, $16,800. 6. Billed customers for delivery services on account, $32,500. 7. Paid creditors on account, $1,400. 8. Received cash from customers on account, $23,770 9. Determined that the cost of supplies on hand was $275 and $475 of supplies had been used during the month. 10. Paid cash to owner for personal use, $5,000. Indicate the effect of each transaction on the accounting equation by listing the num- bers identifying the transactions, (1) through (10), in a column and inserting at the right of each number the appropriate letter from the following list: a. Increase in an asset, decrease in another asset. c. Increase in an asset, increase in owner's equity. e. Decrease in an asset, decrease in owner's equity b. Increase in an asset, increase in a liability. d. Decrease in an asset, decrease in a liability