Using multiple x and y references

Easy, and you can use both tables. I would recommend swapping the columns so X is on the left but you don't have to, it just makes it easier.

You want a scatter chart. All data must be in non-header columns, which it appears to be.

1. Select the data in the first table
2. Create a scatter chart. It should now have one series of data
3. Click on the chart to select it
4. Hold down Command and select the data from the second table. The chart should now have both data series.
5. If you have X on the left in these tables, the only thing left to do is format the chart so it looks the way you want it to.

To swap X and Y

1. Click on one of the data points in your chart
2. Open the Chart Inspector and go to the Series tab
3. Click in the X Data box then go to your table and move the selection box over your X data
4. Repeat that for the Y data
5. Repeat again your other data set

I would use a single table where you add pairs of columns which represent another X/Y pair. Numbers allows you to expand an XY graph data source to include multiple pairs of columns OR share a single X column with multipl Y columns:

After you have you table set up with data and the first row set as a header. Select the range to graph (let's start off with a single series). Select A2 to B4:

now select the XY Graph from the Chart tool. This will plot the first data set. Now select the chart to activate the chart AND reveal the chart data source handle on the table:

First let's move the series name over on column. Click the and hold the tab at the top of the X column and drag it one column to the right:

Now you can add the new series by grabbing the little circle at the bottom-right of the highlighted data source and dragging to the right by a pair of columns: