This combined chart displays 150 months of coffee sales as blue bars on a left y-axis, overlaid with customer counts as a red line on a right y-axis, using two independent linear scales. The visualization also includes grid lines, axis labels, a legend, and circular data points along the customer line for precise value reading. Built with React and D3 v7, the chart renders as SVG, reads data from a CSV file via d3.csv, and constructs the bar and line elements using d3.scaleBand, d3.scaleLinear, d3.axisLeft, d3.axisRight, and d3.line.