Formula for calculating daily total pay when Cumulative hours go over 40

I have a spreadsheet which:

Totals the days hours worked in Column (O9 thru O15)

Totals cumulative hours worked so for in a week in Column (P9 thru P15)

Totals the daily pay in a column (Q9 through Q15).

I have Reg Pay Rate Amount in Cell (R2) and the Overtime Pay Rate Amount in Cell (R4).

What I need is a formula so that when the total in the Cumulative Hours to that point for the week is under 40 it multiplies that days hours x the Reg Rate and when the Cumulative Hours Column goes over 40 hours it will it multiple that days hours x the Overtime Rate.

Keeping in mind that in one day it might be needed to calculate several hours in that same day @ Reg Rate and several hours @ Overtime Rate.

Because we work 12 hour tours per day generally by the end of day four in the week, I have 48 hours total in the Cumulative Column (so that day would need to calculate both rates. It would need to calculate 4 hours @ Reg rate and 8 hours at Overtime Rate)

I am new to this site and not sure if you can upload spreadsheets for you to view because I do not see an option to do it.