Student in need of help

Hello people,

I am trying to make a part where i want to work with a certain pattern and keep the same distances between the two outer holes, i will add a file to this post where u might be able to understand what i mean.

I also want to make a certain formula that if i change the total length of the part i get more or less holes depending on the length, but i want to have it so that the outer holes of my pattern always keep the same distance to the outer circle in the middle. 

I hope u could somewhat understand what i am working with if not i am happy to try to explain it better.

SolidworksGeneral