The distance between two points with coordinates (x₁,y₁) and (x₂,y₂) is calculated through the equation,
distance = sqrt ((x₂ - x₁)² + (y₂ - y₁)²))
We can see that the equation given in this item is very similar to what I have written above only that the (x₂,y₂) is replaced with (3,7).