Development of a exel input formula for microbiology

Tried to open the formulation area of the forum but get an error so posting here and when that is working I can move it.
I need to develop a formula that is used in our microbiology laboratory and the formula on paper is attached as I needed scientific symbols.
total plate count formula.JPG

What exactly is it that you need? A formula in excel that takes these as inputs and calculates, or to just show that formula with the summation symbol, etc as shown in your picture?

not sure but maybe
a1=value of n1
a2= value of n2
a3= value of dilution factor
a4= sum of colonies value
=$A$4/(($A$1+0.1*$A$2)*$A$3)

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