Answer:
6 tsp baking powder is needed if Jack uses 9 c of flour.
Explanation:
Given : Jack's pancake recipe calls for 2 tsp baking powder and 3 c of flour. 
To find : How much baking powder is needed if Jack uses 9 c of flour.
Solution : 
For 3 c of flour baking powder needed = 2 tsp 
For 1 c of flour baking powder needed = 
 tsp
 tsp
Now, we have to find the amount of baking powder needed in 9 c flour.
For 9 c of flour baking powder needed = 
 tsp
 tsp 
 = 6 tsp
Therefore, 6 tsp baking powder is needed if Jack uses 9 c of flour.