The uniform distribution is represented by a rectangle with base length 12-6=6 and height 1/(12-6)=1/6, making the area=1, the total of all probabilities. 10ft is 2/3 of the distance (and area) between 6 and 12 feet, so that’s a probability of 2/3, answer d, because the total of probabilities for ≥10 is the area split off by a vertical line drawn at x=10, where x ranges from 6 to 12. (10-6)/(12-6)=4/6=2/3.