The distance between Mercury and Earth changes a lot because they orbit the sun at different speeds. The longest possible distance (222 million kilometers) is almost 3 times as long as the shortest possible distance (77 million kilometers)! This means the time it takes to get to from Mercury to Earth can change a lot!

In 1973 NASA launched a space probe (Mariner 10) that reached Mercury in 147 days. It did not land on Mercury, but just flew by it. NASA sent a different probe (MESSENGER) to Mercury in 2004 that took 7 years to reach Mercury, but this probe got much closer and entered Mercury's orbit. The second mission took a lot longer because they had to go slow so that they could safely get close to Mercury and not crash into the planet or the Sun.

That depends on how fast you are going. Flying around in the solar system requires the use of the behavior of orbits, as we don't currently have rockets powerful enough to just point at a destination and go there. Our first trip to Mercury took 147 days to arrive. The trip back to Earth would take the same length of time.

The closest Mercury reaches to Earth is about 77.3 kilometers away. Many distances in space are recorded in terms of how fast light travels.

Light can travel to Mercury in about 4.3 minutes, when the two planets are the closest together. For humans, we will have to think about spacecrafts. The fastest spacecraft launched by NASA is the New Horizons mission, traveling about 80,000 km per hour. That means it would take approximately 40 days for a human to reach Mercury from Earth.