Which equation represents a circle is concentric with the circle shown but has a radius that is twice as large?

Equation of a cercle: (x-h)² + (y-k)² = R², where h and k are the center O of the circle, O(h , k)
The equation of the circle shown is:
(x-4)² + (y-6)² = 2² =4
A cercle concentric to the above, should have the same center as the above, but the radius should be greater to 4. 
In your given answers only (x-4)² + (y-6)² = 16 satisfies the question.
So (x-4)² + (y-6)² = 16 is the concentric with (x-4)² + (y-6)²  =4