Tangent line to two circles with VBA

Dear VBA profs,

I've a small issue. I created an excelsheet which works great and now i'm facing a small problem.

I have 2 curves. One with fixed X, Y and radius and the other one is variable in all those settings.
See attachment.(i've removed the confidential data but it's enough for now)

I've already searched the internet and forum and i found this website which shows a VBA code:

http://www.vb-helper.com/howto_circl..._tangents.html

How can i enter this code into my sheet?

Regards,

Erwin