Question

Can someone help me with #2 and I made it clear as possible

Answer 1

Dependent= Amount of money
Independent= Number of cars washed.
This means the amount of money they collect DEPENDS on the number of cars washed.

$300 dollars was collected for washing 30 cars

Answer 2

The independent variable is the variable that changes. In this case, that's the amount of cars washed per day. The dependent variable is the measured variable, which depends on the changed variable. In this case, it's the money collected.
$120/12=$10 per car
$10x30=$300