#### Answer

$(0, 0)$;
$7$ units

#### Work Step by Step

The circle $x^2+y^2=r^2$ has its center at $(0,0)$ and a radius of $r$ units.
The given equation can be written as $x^2+y^2=7^2$.
Thus, the center is at $(0, 0)$ and $r=7$.
Therefore, the missing expressions in the given statement are (in order):
$(0, 0)$;
$7$ units