Excel 2016 makes the combo chart much easier. Please follow the steps below to make a combo chart with 2 Y-Axis. If you work with Excel 2010, please refer here for the detailed steps.
Step 1: Suppose we are making a chart with the data in the Table below, and we want to combine the number of "Met" in column B and "% of Met" in column C together;
Step 2: Highlight the data in the data range A1:C6, and click the "Insert" Tab from the Ribbon;
Step 3: Click "Combo" in the Chart area, then select Clustered Column – Line on Secondary Axis;
Step 4: A combo chart will be created;
Step 5: To change Y-Axis ("Met" or "% of Met"), double click on Y-Axis, then change the value in the Format Axis window (or right-click the Axis, then select Format Axis from the dialog box);
Step 6: To change the Chart Tile, double click and then replace the words with the correct ones.