This area chart visualizes the average quantity of laptops sold at different cost levels, using data loaded from a CSV file. It shows a smoothed line and a semi-transparent filled area beneath it, representing the trend of average sales as cost increases. The chart is built with D3 v7, using `d3.csv` to fetch the data, `d3.rollups` to compute averages, and `d3.area` with `d3.curveMonotoneX` for the filled region, alongside `d3.axisBottom` and `d3.axisLeft` for the axes.