Without the hint that I gave, my readers would probably have been
unanimous in deciding that Mr. Perkins's income must have been £1,710.
But this is quite wrong. Mrs. Perkins says, "We have spent a third of
his yearly income in rent," etc., etc.--that is, in two years they have
spent an amount in rent, etc., equal to one-third of his yearly income.
Note that she does _not_ say that they have spent _each year_ this sum,
whatever it is, but that _during the two years_ that amount has been
spent. The only possible answer, according to the exact reading of her
words, is, therefore, that his income was £180 per annum. Thus the
amount spent in two years, during which his income has amounted to £360,
will be £60 in rent, etc., £90 in domestic expenses, £20 in other ways,
leaving the balance of £190 in the bank as stated.