Final answer:
An observer who sees the North Star 30° above the horizon is located at 30° latitude north.
Step-by-step explanation:
An observer who determines that the North Star (Polaris) is located 30° above the horizon is located at 30° latitude north. The altitude of the North Star above the horizon is equal to the observer's latitude. For example, if an observer is at 30° latitude north, Polaris will be located 30° above the horizon.