Given that spending for a certain household will always include a base amount of $1000/month, and that additional spending is equal to half of any income earned, we can predict household spending with a model y=b+mx, where

With the straight line equation, we can assume y = household spending, x is the income earned monthly, and b would be the base amount spent per month ($1000). m = 1/2 of the income that is spent (additional spending).

Therefore our equation takes shape as follows:

y = 1/2 ($income) + $1000