(1 point) Answer the following questions about the sphere whose equation is given by
$x^2 + y^2 + z^2 - 10x + 8y = 23$.
1. Find the radius of the sphere.
Radius: $r =$
2. Find the center of the sphere. Write the center as a point $(a, b, c)$ where $a$, $b$, and $c$ are numbers.
Center: