In Spanish a personal A used when the direct object is a person
Example: Brooke llama A Elsa
In English this means Brooke calls Elsa
But in Spanish it is being use mostly at a person but can also be use at an object
Hope this helps :3
The direct object pronoun would be "la" because la gasolina is feminine. In a sentence you could say:
"La compro en la estacion de servicio."
Direct object pronouns are placed before the verb generally.
You need to add the "audio" so the question can be answered.