olmuştu

In a sentence

• Dün hava çok kötü olmuştu.

  Yesterday, the weather had turned very bad.

  In this sentence, 'olmuştu' is used to refer to an event that had occurred in the past before another past referencing event.

• Etkinlik başladığında herkes yerine oturmuştu.

  By the time the event started, everyone had taken their seats.

  Here, 'olmuştu' is part of the past perfect tense, indicating actions completed before the past action of 'the event started'.

• Bu problem zaten önceden çözülmüş olmuştu.

  This problem had already been solved earlier.

  In this sentence, 'olmuştu' expresses that a resolution to the problem had been achieved prior to another past event or reference.