Final answer:
The landing distance at a high elevation airport on a hot day is longer because both high elevation and high temperatures result in lower air density, which decreases lift and requires more distance to land safely.
Step-by-step explanation:
The landing distance at a high elevation airport on a hot day is likely to be longer due to a combination of factors. High elevation means that the air pressure is lower, which decreases the air density. Hotter temperatures also contribute to lower air density. Aircraft rely on the density of the air to produce lift. Thinner air at high elevations and hot temperatures means that more speed and thus more runway is required to produce the necessary lift for a safe landing. Therefore, the correct answer is (b) longer, due to high elevation, high temperature, and lower air density.