Here is a puzzle I have been trying to solve for a long time. It was given at work as a monthly puzzle but the solutions were never released.
If I can resurrect this unsolved puzzle, I believe I have an answer:
N + L = A
At first I wondered whether the answer would be:
E, since the answers appeared to be spelling out 'WALES' and the question's blurb points to North Wales (Gogledd Cymru).
However, I could not come up with a way to make this work, so I'm pretty sure it's a red herring. Instead, I then noticed a different set of connections...
P + L = W
The internet country code for Poland is .pl and its capital, Warsaw, begins with W.
T + R = A
The internet country code for Turkey is .tr and its capital, Ankara, begins with A.
P + E = L
The internet country code for Peru is .pe and its capital, Lima, begins with L.
Which means that for N + L = ?, we equivalently have:
the internet country code for the Netherlands (.nl) so the answer could be the first letter of its capital, Amsterdam i.e. A.
A pointer towards this solution might be:
The blurb's mention of 'riddles and code', which could point towards country internet codes...
I realise you and your colleagues have probably moved on from this question a long time ago but hopefully this answer might provide some closure to this unanswered puzzle if you agree my solution might be correct! :)