Jennie is making popcorn. The recipe calls for 12

 cup of butter, 3 tablespoons of kernels, and 1 teaspoon of salt. If she uses 10 tablespoons of kernels, how much butter does she need? Round your answer to the nearest hundredth.

To find out how much butter Jennie needs when using 10 tablespoons of kernels, we set up a proportion:

12 cups/3 tablespoons = x cups/10 tablespoons

Cross multiplying, we get:

3x = 12*10
3x = 120

Dividing both sides by 3:

x = 120/3
x = 40

Therefore, Jennie needs 40 cups of butter when using 10 tablespoons of kernels.