A car manufacturer tested the gap between the doors and the body of a new car using 18 samples in millimeters as shown: 1.7, 1.9, 1.4, 1.4, 1.5, 1.7, 1.1, 1.6, 1.9, 1.4, 1.5, 1.5, 1.6, 1.5, 1.3, 1.8, 1.6. What is the average gap between the doors and the body of the car?