Answer:
- 15 + 5 
 - 5(3 + 1) 
 - (5)(3) + (5)(1)
 
Explanation:
Apparently, the model is expressing the total number of acres of corn in the two mazes. The two mazes total 20 acres, so the expression needs to be something that gives a result of 20. 
Of the choices offered, the ones shown above have a value of 20.