Scheduling for driver's education students

So I am trying to do a sheet for my drivers training company. Each student must do 6 individual 1 hour drives to graduate. What i was trying to do is calculate, based on the available instructor hours, how many of each drive per week I should be expecting. So in my example i have 15 students and have the necessary 90 hours of instructor time available. So on week one we should have 15 drive #1s and the remaining will be drive #2s. My sheet worked out ok until i got down toward the bottom and it gave me a total of 18, which is more than the number of students.

So maybe there is a better way to calculate? Maybe even remove the hard drive numbers and have a formula that says if x then drive 1, after that drive 2 etc etc. IDK looking for fresh insight here

I have plugged some manual numbers in read to show what i am hoping to get to roughly. Highlighted in yellow i think is only area that needs work unless you see something else.

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