What is the standard form of the equation of the given circle with center a(4, 8)?

a.) (x - 4)^2 + (y - 8)^2 = 2.5
b.) (x + 4)^2 + (y + 8)^2 = 6.25
c.) (x + 4)^2 + (y + 8)^2 = 2.5
d.) (x - 4)^2 + (y - 8)^2 = 6.25

The standard equation of a circle is expressed as (x - h)^2 + (y - k)^2 = r^2 where (h,k) is the center of the circle and r is the radius of the circle. When center is at (4,8), then the left side should be (x - 4)^2 + (y - 8)^2. i guess the radius is 2.5 so that r^2 is equal to 6.25. Hence the answer is D