Final answer:
The length of the radius of circle f is 3.
Step-by-step explanation:
The equation of the circle is given as (x-6)² (y -8)² = 9. To find the length of the radius, we need to rewrite the equation in the standard form, which is (x-h)² + (y-k)² = r², where (h, k) is the center of the circle and r is the radius.
Comparing the given equation with the standard form, we can see that the center of the circle is (6, 8) and the radius is 3. Therefore, the length of the radius of circle f is 3.