Given two points A(x₁,y₁) and B(x₂,y₂) the distance betwen these points will be:
dist(A,B)=√[(x₂-x₁)²+(y₂-y₁)²].
We have these points: A(7,9) and B(3,12); its distance will be:
dist(A,B)=√[(3-7)²+(12-9)²]
=√(4²+3²)
=√(16+9)
=√25
=5
The distance between these points will be: B. 5 units.