IMAS 2022 — Upper Primary Grades 5–6 — Round 1 Question 18

Charles has a farm on a $3\times3$ plot. The farmhouse is in the central lot, and pigs are kept in the eight other lots, with at least one pig in each lot. The total number of pigs in the three lots on any of the four sides of the farm is 9. An example is shown in the diagram below, where the total number of pigs is 28.

Which of the five numbers below CANNOT be the total number of pigs?