Answer:
2 Cups of baking soda for 4 cups of flour.
Explanation:
If we look at the chart, we can see that the X-Axis of the chat is what measures the flour. If we go to 4 on the X-Axis for 4 cups of flour, we then can go straight up the Y-Axis from the 4 plot on the X-Axis.
If we go up until we meet the line on the Y-Axis and plot a point here, we can then trace over the X-Axis until we meet (0,2) so therefore the answer to your question is 2 cups of baking soda for 4 cups of flour.