To determine how much baking soda Lisa should add to 9 pounds of flour, we first need to find the ratio of baking soda to flour from the original mixture.
Lisa uses 2 tsp of baking soda for 6 lbs of flour. We can find the amount of baking soda per pound:
\[ \text{Baking soda per pound} = \frac{2 \text{ tsp}}{6 \text{ lbs}} = \frac{1}{3} \text{ tsp/lb} \]
Now, we can multiply the amount of baking soda per pound by 9 lbs to find out how much baking soda is needed for 9 lbs of flour:
\[ \text{Amount of baking soda for 9 lbs} = \frac{1}{3} \text{ tsp/lb} \times 9 \text{ lbs} = 3 \text{ tsp} \]
Therefore, Lisa should add 3 tsp of baking soda to 9 lbs of flour.
The correct response is:
3 tsp