thanks for ur reply Patrick

On Fri/Sat/Sun only 2 shifts will work & yes always a 24 hour shift. so on these days each shift will work 12 hours

I tried a simple formula to find out how many shifts A, B work if they have to cover 60 hours a week & the average would be 9 hours a day, & for shift C working no less than 48 hours a week it would be 6 hours a week.

Every month the shifts change so as the moring shift takes the afternoon & the afternoon takes the nite & the nite takes the moring.

Thanks