Answer: 4
Explanation:
It creates a right triangle.
one leg is 3
the hypotenuse is 5 (the key here is to know that the radius is 5 and can be moved anywhere
the last leg is BC which is what you are looking for
so use pythagorean
c²=a²+b²
5²=3²+BC²
25-9=BC²
BC=√16
BC=4