use backward formulas

[Shama85]

i am stuck here with a formula, i need to do a special sum formula, i need it to be as variable as possible.
so the issue

is that i want to sum the production on different operations
every operator has a different number of operators
so first operation i want to sum at cell E6, rows from E1:E5
second operation E14 rows from E7:E13
i want to make a variable formula that can choose this value without typing the range every time. note that at total columns i have the word "Total" at D column, this may be used to identify the range.
thanks for your help, i tried to add a photo for the sheet not sure if it uploaded or no

 

[Shama85]

i found the answer in a previous topic i just modified the formula to match my requirements

SUM((INDEX(N$1:N15,(LOOKUP(9.99999999999999E+307,1/($L$1:$L15="total"),ROW($L$1:$L15))+1))):N15)

index at the sum formula will replace the cell choice you can put either before or after ":"
N15 is the number of the cell i want to do the sum, and upwards i wanted to stop when it sees the word "Total" in column "L" and choose the next row number
what i do not under stand is this value 9.9999999 E+307
if some one can explain it will be great

here is a link of the sheet photo for more understanding
https://drive.google.com/open?id=1el-bqo1zLO4Ri58_Dxy8RaBK07U5plJg