It's impossible to say exactly how many Earths would fit inside a supergiant star without knowing which supergiant star we're talking about. Here's why:

* Supergiants come in many sizes: Supergiant stars are incredibly large, but they vary greatly in their diameter. Some are only a few times larger than our Sun, while others are hundreds of times bigger.

* Stars aren't solid: Stars are made up of gas and plasma, so they aren't like solid objects where you can just "fit" things inside. Their density is also variable.

Here's an example:

* Betelgeuse: A famous red supergiant in the constellation Orion, is about 800 times larger than our Sun in diameter. That means it's roughly 600 million times bigger in volume than the Sun.

* The Sun: The Sun is about 109 times larger in diameter than Earth.

Very roughly, you could say that Betelgeuse is big enough to hold approximately 100 million Earths. But this is just an estimate.

Important Note: This is a very simplified way to think about it. The actual process of fitting Earths into a star is complex and involves dealing with the star's changing density and gravitational forces.