To find out how much baking soda Lisa should add to 9 lbs. of flour, we can set up a proportion based on the amount of baking soda she added to the 6 lbs. of flour.
Given that:
- 2 tsp of baking soda is used for 6 lbs. of flour.
We can find the amount of baking soda needed for 1 lb. of flour: \[ \text{Baking soda per lb.} = \frac{2 \text{ tsp}}{6 \text{ lbs.}} = \frac{1}{3} \text{ tsp/lb.} \]
Now, for 9 lbs. of flour, we can multiply the amount of baking soda per lb. by the total number of lbs.: \[ \text{Baking soda for 9 lbs.} = \frac{1}{3} \text{ tsp/lb.} \times 9 \text{ lbs.} = 3 \text{ tsp}. \]
So, Lisa should add 3 tsp of baking soda to 9 lbs. of flour.