whats the distance formula?

Try the pythagorean theorem.

sqrt{(x₂-x₁)²+(y₂-y₁)²

For example, you have the coordinates of (5, 4) and (-3, 8)

sqrt{(4-8)²+(5-(-3))²

sqrt{-4²+8²

sqrt{16+64

sqrt{80

4sqrt{5