A French professor of mathmatics retired without a pension, but his wife said "dont worry dear, I will go out to work"

The first day she earnt 15 dollars
the 2nd day 150.
the 3rd day 1500
the 4th day 15000

total 16665

She handed over $16000 to her retired husband and he said you owe me £665.

She said how come?

The men were like this 6666
but later they were 9999
total 16665