From the question we can deduce that, the squares shaded in red represent the area tomatoes are planted in the garden.
The squares unshaded represents the area corn is planted in the garden.
Observe carefully that the total squares shaded in red are 24 (that is 4 by 6 OR 4 times 6). The unshaded squares total 18 (that is 3 times 6).
Each unit (or each square) is 1 square foot. This means on Nora's garden, she has tomatoes planted on 24 square feet. Also she has corn planted on 18 square feet.
Therefore, the difference between both areas is
Difference = 24 - 18
Difference = 6
ANSWER:
There are 6 more square feet of tomatoes than corn in Nora's garden.
The correct answer is option D