Drivers pay a toll to pass over a busy bridge, and there are many toll booths that collect money. The city manager counted the total number of cars waiting to pay their tolls at 15-minute intervals during the day for a total of 50 observations. The histogram below shows the results. A histogram titled Bridge Toll Booth Traffic has number of cars in line on the x-axis and frequency on the y-axis. 0 to 10, 4; 10 to 20, 13; 20 to 30, 18; 30 to 40, 8; 40 to 50, 5; 50 to 60, 1. Which interval contains the median number of cars in line? 10–20 cars 20–30 cars 30–40 cars 40–50 cars