When your cleaning terraced houses and they are rows of houses right next to each other 40 houses isnt hard.
Wor Lass and I have a street of 26 terraced houses, all pretty much next door to each other; they're priced between £7 and £10 each and it takes us about five hours to do the lot (not including a lunch time break); that's me WFP tops and Wor Lass following behind with a squeegy.
When I get so far ahead of her, I return with a squeegy; we're pretty quick and have both been window cleaning for five years.
That works out as 5.2 houses per hour between the two of us
(in five hours, with an hours lunch on top) and it's a days work for both of us; though I may do more work after I drop her off home.
So I can't see how one person can clean 40 terraced houses in one day. That works out as 5 houses per hour for one person on an
eight hour day without a break, and, if you can clean 5 terraced houses in an hour (and you must be VERY VERY VERY quick to do that; no talking to customers either) I reckon that's pretty much impossible to sustain; day in, day out; week in, week out.
There's some waffling going on here, or these 40 houses are doll's houses!