Question

radius =

diameter = 26

Explanation:

Step1: Recall radius-diameter relation

The radius $r$ of a circle is half its diameter $d$, so $r=\frac{d}{2}$.

Step2: Substitute given diameter value

Substitute $d=26$ km into the formula:
$r=\frac{26}{2}$

Step3: Calculate the radius

$r=13$

Answer:

radius = 13 km
diameter = 26 km