An apartment building has a parking lot with 12 parking spaces for tenants. At 6 a. m., all 12 spaces were full. At 8 a. m., the number of cars in the lot had decreased by 4. By 9 a. m., there were no cars left in the lot. Use the number line to show each change in the number of cars in the parking lot. What integer represents the change in the number of cars between 8 a. m. and 9 a. m.? (need answers quick)