Everyday the company charges $12 you for renting the car. So, if you rent the car for 7 days then the cost will be $84. $12 * 7 = $84
And for every mile you drive, you pay $0.30. So, if you drive for 100 miles you will pay $30.
Now we can put this into an equation.
y = 12x + 250(0.30)