Formulas in Excel
 

I am very new to excel and could use some help trying to do a formula. On my
worksheet Col B(Hrs Worked Today). Col C(Total hrs worked last 7 days). Col
D(would be 70 hrs minus Col C). Col E(Total hrs worked last 8 days). I know
the basic formulas to complete the above steps.

B1 C D E
10 50 20 60

If I take a 34 hr rest period, I get a fresh 70 hrs which would put col c&e
at 0 and col d at 70. I need a formula that will do this when I put an
idenity (reset or -34 etc.) in B2