Answer:
Yo nunca había trabajado antes de aceptar éste trabajo
Step-by-step explanation:
This sentence is in the pluperfect form, or preterito pluscuamperfecto in spanish. Used to refer to an action at a time in the past that happened earlier than a time in the past already referred to, in other words, it`s the past of the past. In this sentence, Yo nunca había trabajado antes de aceptar este trabajo (I had never worked before accepting this job), Yo nunca había trabajado (I had never worked) is the furthest event in the past, and antes de aceptar este trabajo (before accepting this job) is a more recent event, but also in the past. We can infer that the subject already accepted the job in a recent moment in the past. It`s conjugated with the verb Haber (to have) as an auxiliary in front of the main verb. The conjugation of the auxiliary varies depending on the pronoun, however the conjugation of the main verb remains the same for all pronouns. It's very similar to the Past perfect tense in English.