number of days based of number of weeks

Hello,

In my school we manual calculate when a student is suppose to graduate(contract graduation date),and decided to use excel now. The students goto school 7 hours a day except on saturday(6 hours) for a total of 34 hours/week in the school I am having problems with. The others schools its 7 hours a day each day so I just divided the numbers of required hours(1500)by 7 to give me the amount of days(214.3) to put in excel(networkdays)formula. I can not figure out many days to put in(daysrequired) since I just cant divide by 7 in the school that does 6 hours on saturday. The reason I want a formula instead of putting a standard number is because students came with hours already,and we deal with hundreds of students and this was save tons of time. I dont know if I am making this too difficult for myself,but a have a block. The formula I came up with was the saturday is 20% of the week so will account for 20% of the total hours(300) and so divide that by 6 and the rest(1200) by 7 to give me 222 days to put in days required. Would that be a correct way or is there a better way???

Thanks