Sunny's garden has 9 tomato plants, 5 pepper plants, 3 squash plants, and 6 pumpkin plants. for every 3 tomato plants in sunny's garden, there is 1 plant.

9 total tomato plants  /  3 plants = 3

from the list of plants there are 3 squash plants

3 squash plants x 3 tomato plants = 9 total tomato plants

 the answer is Squash Plants