Point B is a point of tangency. Find the radius r of ⊙C.

Since Point B is a point of tangency, there is a right angle being created on the edge of that circle.

This means that the Pythagorean Theorem can be applied to solve for r.

*A common mistake here is distributing the square to both 16 and r, whereas you should be multiplying 16+r by itself (FOIL).*

The s cancel.

The radius r of Circle C is 10.

Hope this helps!

2.83941151 would be the answer you're looking for! : )