#### Answer

center: $(0, 0)$
radius = $4$ units
Refer to the image below for the graph.

#### Work Step by Step

RECALL:
The standard form of the equation of a circle with a center at the origin and a radius of $r$ units is:
$x^2+y^2=r^2$
The given equation can be written as $x^2+y^2=4^2$.
This is the same form as the standard equation above, so its center must be at the origin and its radius must be 4.
Thus:
center: $(0, 0)$
radius = $4$ units
To graph the equation, do the following steps:
(1) Plot the center $(0, 0)$, and then locate the points four units to the left, to the right, above, and below the circle's center.
These points are:
$(-4, 0)$
$(4, 0)$
$(0, -4)$
$(0, 4)$
(ii) Connect the four points (excluding the center) together using a curve to form a circle.
(Please refer to the attached image in the answer part above.)