Hoy many moons does mercury have?

Unfortunately, the answer is no, Mercury has no moons.

But if moons are so common in the Solar System, and even Pluto, which is smaller than Mercury has moons, why doesn’t Mercury have moons?

The Earth got its moon when a Mars-sized object crashed into our planet, and the debris collected into the Moon. It’s possible that a similar impact happened to Mercury early on in its history. But the moon would have either drifted away or crashed back down onto the surface, because it’s not there anymore.