According to Luke, how many demons had gone out of Mary Magdalene?

Answer: Seven

Mary called Magdalene, from whom seven demons had gone out, traveled with Jesus and the Twelve.

“Soon afterward, Jesus traveled from one town and village to another, preaching and proclaiming the good news of the kingdom of God. The Twelve were with Him, as well as some women who had been healed of evil spirits and infirmities: Mary called Magdalene, from whom seven demons had gone out,”— Luke 8:1-2 (BSB)