Learn Spanish (Latin America): La fábrica solía transformar los vehículos viejos. - The factory used to transform the old vehicles.

Solía is the imperfect form of the verb soler, which means 'to usually do something'. In the past tense, it translates perfectly to 'used to'. It acts as a helper verb and is always followed directly by an infinitive (the unconjugated verb), which is why we use transformar right after it.

Could I just say La fábrica transformaba... instead of using solía?

Yes! La fábrica transformaba also translates to 'The factory used to transform' (or 'was transforming'). Using solía transformar is just a great way to put extra emphasis on the fact that this was a regular habit or routine in the past.

Do I need to use a preposition like a or de between solía and transformar?

No, and this is a great thing to memorize! Unlike verbs like empezar a (to start to) or tratar de (to try to), soler connects directly to the infinitive. It is always solía transformar, never solía a transformar.

Why do both fábrica and vehículos have written accent marks?