Answer:
Incan suspension bridges 6 - these were simple bridges that were not so difficult to make.
Incan terraces 5 - they were crucial for the Incan economy, but they are not so difficult to figure out, the proof is that many cultures in Asia also had terraces for the cultivation of rice.
Aztec Chinampas 4 - they were more or less like the Incan terrances, but on the water.
Mayan step -pyramids 3 - Pyramids are quite difficult to build, and the Mayan pyramids are among the best examples in the world, along with Egyptian pyramids, and Aztec pyramids.
Aztec causeways 2 - The Aztec causeways were true feats of Aztec enginering: water canals that for example, allowed navigation around the Aztec capital: Tenochtitlan, on the lake of Texcoco.
Mayan calendar 1 - The Mayan calendar is a great feat of math, astronomy, and science in general. Modern scientists are still fascinated by its complexity and accuracy.