@Chrono79, @awesomead, thanks for your rapid answers, it was needed to type exactly as the author wrote:
"var firstName = {A: 'Alpha', B: 'Beta', C: 'Cache' ...}
var surname = {A: 'Analogue', B: 'Bomb', C: 'Catalyst' ...}"

So, "firstName" and "surname". Not "surName" as I typed.

Could be better! Marked by author as solved but keeps returning: "ReferenceError: surName is not defined". If the two arrays can not be loaded into code wars, then the author must put into the description, even if this occupy a lot of space. This way we can copy into work area in order to use them and solve with our code.

Wow! I had tottaly forgotten this math principle. This is a great and simple solution!