Excel If statement to make given Column a negative value

Hi,
I am trying to create a formula in excel to make a given column a negative number.
The example used is:
I have two columns A and B
Column A has text in it so Peter, John, David, Liam
Column B has numbers in it and so 10, 20, 40, 60, 80

The formula I need is: If Column A = Peter, John make Column B a negative number in red
so something like =IF((A1-A15)="Peter","John" Then ((B1-B100=-....))

Hope you can help

With a formula you need another cel/column:
=if(or(a1="peter",a1="john")=b1*-1,b1)

Please provide a sample sheet showing requested result

Hi ExcelITtroubleshoot

In C1 and copy down:

Formula:

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Select C1:C8, conditional formatting on the home tab and the rule: =$C1<0 format as required.