The correct answer is A) (x-5)²+(y-10)²=12².
The graph of possible locations would be a circle, since he could be in any direction. 12 would be the radius, since he could be 12 miles away. The center of the circle would be his last location. The equation of a circle is given by:
(x-h)²+(y-k)²=r²
Since (5, 10) is the center and 12 is the radius, this gives us
(x-5)²+(y-10)²=12²