8
Step-by-step explanation:
Since AB is tangent to the circle, ABC is a 90 degree angle. Using either knowledge about special triangles (3-4-5) or the Pythagorean theorem, BC will equal 8.
Hope this helped.
pretty sure she did something wrong in the 1st step, it specifically said to do 6.1-4.5, but she changed the parathenesis, resulting in a different answer