If you count the zeros it’s
one billionth
45 new houses.....last month 1/3 were sold....
1/3(45) = 45/3 = 15 houses sold last month
this month, 1/5 of the remaining houses were sold...
remaining houses left are (45 - 15) = 30
1/5(30) = 30/5 = 6 houses sold this month
houses left : 45 - 15 - 6 = 45 - 21 = 24 houses remain <==
Nonprportional is what I would think
I'm assuming this is multiple choice and you forgot to post the answers. I'll take a guess and say it probably looks something like this:

Because you can't take the square root of a negative number without getting an imaginary result, resulting in the function having a closed domain limit.