Answer: Please the terms do not match the definitions.
Please see below for the appropriate terms which match the given definitions.
Step-by-step explanation:
A document that creates a legal obligation to buy and pay for goods or services ----Purchase order
A purchase order is defined as a contract or agreement between a buyer( buisness or company) and a seller who is usually a vendor to supply goods or services based on aggrement on the specific product or services, specific quantity for a specific price to be paid by the buyer when delivered .
b)The method used to maintain the cash balance in the petty cash account----- Imprest Fund
An imprest Fund is also known as Petty Cash fund which carries a fixed amount used by Buisnesyses to cover small routine expenses and are replaced or replenished to always maintain the fixed amount.