10 inches because at 4 pm it was 6 inches but since it says it increases 4 inches during the times 4 PM through 6 PM it should've gone up another 4 inches. 6 plus 4 equals 10. ?????????
Biased because the survey was conducted in a limited field of people aka health club which does not include other people, perhaps an unhealthy club? Or the people who are not a part of the health club? Or people who do not care about their health?