Chapter P - Preliminary Concepts - P.3 - Informal Geometry and Measurement - Exercises P.3 - Page 25: 45

10.9

We are told that line segment AD is trisected by the three smaller line segments. This means that each of the smaller line segments is 1/3 of the total length of line segment AD. From this, it follows: $$ L_{AB}= \frac{32.7}{3} \\ L_{AB} = 10.9 $$