To determine how much you earn for washing 7 cars, we first need to find out how much you earn per car.
You earn $48 for washing 8 cars, so:
\[ \text{Earnings per car} = \frac{$48}{8 \text{ cars}} = $6 \text{ per car} \]
Now, to find out how much you earn for washing 7 cars, we multiply the earnings per car by the number of cars:
\[ \text{Earnings for 7 cars} = 7 \text{ cars} \times $6 \text{ per car} = $42 \]
Therefore, you earn $42 for washing 7 cars.