Why is مُعَلِّمِيَّ genitive in سَلَّمْتُ عَلَى مُعَلِّمِيَّ?

Noun Case Class 9 — Sound Masculine Plural with My

• Because the verb is in the past
• Because of the preposition ʿalā
• Because of the subject tāʾ
• Because every plural is genitive