price per house : $250,000
number of houses: 9
To find how much he will earn (y) we have to multiply the price per house by the number of houses (x).
y = 250,000 x
Where x is the independent variable (number of houses) and y is the dependent variable (earnings)
Replacing x by the number of houses:
y = 250,000 ( 9) = $2,250,000