Answer:
The correct answer is When did you buy yourselves a new car?
Step-by-step explanation:
Second Person pronouns are those that are used to refer to an individual (singular) or more individuals (plural), without the speaker being involved.
This is the case of the example When did you buy yourselves a new car?
That is reflexive means that the subject, and the complement of the verb will be equal. In other words, the subject will do the action for himself, in this case: yourselves. (you do something for yourself).
The second person pronouns include the following pronouns, both plural and singular: you, yours, yourself, yourselves.
In the case of the sentence When did we buy ourselves a new car? The speaker is included, therefore it is not second person but first person.