How to calculate the required number of PRBs for LTE?

Question

Mathematics

Hello. My task is to calculate the required number of PRBs for:
In the period from 0 to 100 TTI - there is 1 subscriber in the sector (VoLTE traffic)
In the period from 20 to 100 TTI - a subscriber watching TV (MPEG-4) appears in the sector
B period from 50 to 100 TTI - a subscriber appears in the sector, pumping something.
It is necessary to calculate the required number of PRBs for each traffic profile at different CQIs (select 3 limit options: CQI=1, 8, 15).
a=0.5
By formula

My question is mainly about the relationship of PRBsTTI (N) with the number of subscribers and the choice of CQI.
Thank you very much if someone paid attention.