It's a scatter plot, so your data are split across the points (each point is independent and contains its own unique items - it doesn't overlap with any others).

So, you can find the number of items at each price point (for every scatter point, note the y-value) and sum them. This is a bit tedious to do since you'll have 10 values for each store, but it is very obvious from looking at the points that Store 1 will sell more items (their points are higher on average, indicating more items per point).