18. Find the radius of the circle whose equation is $(x+3)^{2}+(y-7)^{2}=289$.

Step 1 ：Given the equation of a circle: \((x+3)^2 + (y-7)^2 = 289\)

Step 2 ：The radius squared is 289, so the radius is \(\sqrt{289}\)

Step 3 ：Calculate the square root of 289: \(\sqrt{289} = 17\)

Step 4 ：\(\boxed{17}\) is the radius of the circle.