Answer:
15
Step-by-step explanation:
Something divided into thirds will be divided into three equal pieces.
One hall way divided into thirds would be 3, 1 * 3 = 3
two hallways divided into thirds would be 6, 2 * 3 = 6
three hallways divided into thirds would be 9, 3 * 3 = 9
four hallways divided into thirds would be 12, 4 * 3 = 12
five hallways divided into thirds would be 15, 5 * 3 = 15
