Green’s Dictionary of Slang

five shillings, a crown.

1859		Hotten Dict. of Modern Sl. etc. 123: Beyond this amount [i.e. flatch yennork: a crown] the costermonger reckons after an intricate and complicated mopde. Fifteen shillings would be Erth-evif-gens, or, literally, 3 times 5s. [etc.].
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 23/1: Ewif-gen ... Crown. [...] The costermongers still further complicate their slang by a mode of multiplication. They thus say, ‘Erth Ewif-gens’ or 3 times 5s., which means of course 15s.
1873		Sl. Dict. [as cit. 1859].
1892		Lloyd's Wkly Newspaper 3 Jan. 6/5: Sidling up to Joe he whispered, 'Ewit gens'.
1935		R.T. Hopkins Life and Death at the Old Bailey 66: Ewif-gen – Five shillings.