Salam Alaikum wa rahmatullahi wa barakatuh Ustadha,
This is what I found regarding the question we had in class today about the interrogative noun: كَمْ
كَمْ is used to ask about numbers (how many) and quantities (how much).
When كَمْ is used to ask about a number (how many), the noun following it is in the accusative case (mansoob), with a fatħah vowel-ending.
For e.g كم طفلاً , كم كتابً
When كَمْ is used to ask about the quantity (how much), the noun following it is in the nominative case (marfoo'), with a đammah vowel-ending.
For e.g كم درجةُ الحرارةِ , كَمْ عُمْرُكَ
I hope this is helpful in sha Allah.
I hope this is helpful in sha Allah.
Jazakum Allahu khairan
Ref: https://www.madinaharabic.com/arabic-language-course/lessons/L042_005.html