Bashed throught this but found it a bit of a slog, to be honest. There seemed to be a few steps where you had a process quite a lot of sums in order to check possibilities so I resorted to Excel for those.
It's possible that there was a more elegant way to solve it but I had my jab yesterday so everything is a bit foggy today.
Anyway, thank you Zag as I do find numericals are a nice change of pace!