Seems to derive from nursery rhyme "How many miles to Babylon?", which likewise specifies 3=score & 10, and also contains the 'candle-light' question. Good entries in Wiki & in the Opies' Ox Dict of Nursery Rhymes [#26]. The Opies suggest that Babylon might be a corruption of Babyland — tho some religious or Biblical input seems likely to me also. 'Dublin', in both above variants, also has quite a strong assonantal relationship to 'Babylon', hasn't it?