Units are not compatible?

[Astolbon]

Hi!
I have some trouble getting a equation work properly and wonder if someone here are able to help me?
So the problem is that x is a length in meters, but if i add it in to the equation it cant give any solutions to the ones in the green box. But if i remove the meter unit i cant get the ones in the blue box????
Leff:=2.1m

Thanks in advande
/John

[Fred_Kohlhepp · Accepted solution]

Your second definition is right, then you give the functions a length as an input:

[Astolbon]

Thank you so much for your help, i have spent hours to figure this one out but couldn´t do it!
It works fine now 🙂

/John