Dificulty of skill rolls

I was trying to set some fair targets for skill rolls by some characters and I thought I would look at the 5th edition rules for guidance and there does not seem to be any.
The skill rolls in question where awareness rolls , there was no opposed rolls to compare with and I could not see any guidance for even something like easy/moderate/hard

ArM5, page 7
0+ Trivial
3+ Simple
6+ Easy
9+ Average
12+ Hard
15+ Very Hard
Etceteras...

So I failed to look at P7, and had no luck with the index. I thought I had seen something but I thought it could have been 4th ed