Exegesis:

hina ekbalōsin auto ‘that they cast him out.’ hina points to the intended result. For ekballō cf. 4.29.

kai ouk ēdunēthēsan ‘and they could not.’ The aorist tense, referring to a punctiliar event, implies that they tried but failed.

Translation:

In Foe ‘begged’ and ‘could’ are in the near past tense, implying that the conversation referred to took place earlier on the day of speaking.

Cast out, or, ‘caused to come out,’ see 4.35.

They could not, or, where necessary, ‘they were not able to do so (or, to do what I asked, or, to cast it out).’

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.