A forced-choice design is often used to compare the attractiveness of pheromones to insects. A Y-tube is used. The pheromone is place on one branch; the control on the second branch; and the insect on the third branch. The insect then chooses one of the two branches. Suppose that 28 of 70 insects choose the pheromone branch. What is the z-score for testing the hypothesis of no-preference?