So guys i'll try to resolve a problem with slope calculation in percentage, to substract from a value I have exploring the web but found nothing really helpful.
Name:  axe balancier 1.jpg
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the problem is:
I will find the value of climb with following numbers in red diam 4.2mm/ length of the slope 0.45 mm /need to know the 8%
please if you can help i will thankful all of you, my geometrics are rusted

If i take the the full diam it seems not work either if i use the circle of radius i was lost

I know it is possible to resolve by the cross multiplication but can't remember if it works for finding the result or solely for finding the percentage if you don't know it.