Need help with conditional formula

I am creating a sales per day/week worksheet for my reps to keep track of their sales. I have created the sheet that they only have to enter in what they have sold and it automatically calculates what they have sold per hour in the day, and what that makes their weekly total.

The problem is sometimes they will work 5 days, sometimes 4, sometimes 6 or 7.

im trying to fix the weekly average formula to divide by 7.5 for 1 day worked, 15 for 2, 22.5 for 3, etc all through 7...

this is the formula I have now, obviously it doesnt work

=IF(COUNT(B7:H7)=1,SUM(E42,E75,E110,E143,E175,E207,E238)/7.5,IF(COUNT(B7:H7)=2,SUM(E42,E75,E110,E143,E175,E207,E238)/15,IF(COUNT(B7:H7)=3,SUM(E42,E75,E110,E143,E175,E207,E238)/22.5,IF(COUNT(B7:H7)=4,SUM(E42,E75,E110,E143,E175,E207,E238)/30,IF(COUNT(B7:H7)=5,SUM(E42,E75,E110,E143,E175,E207,E238)/37.5,IF(COUNT(B7:H7)=6,SUM(E42,E75,E110,E143,E175,E207,E238)/45,IF(COUNT(B7:H7)=7,SUM(E42,E75,E110,E143,E175,E207,E238)/52.5)))))))

Little help please!