Respuesta :

SJ2006
It would be: Kn + 4f = 9
kn = 9 - 4f

n = (9-4f) / K

Hope this helps!
Kn+4f=9
Divide 9 by 4
Kn+f=2.25
Kn=2.25-f
n=(2.25-f)÷K