To solve this problem you must apply the proccedure shown below:
 1. You must apply the formula for calculate the area of a equilateral triangle and clear the side of the triangle (s):
 A=(√3)s²/4
 s²=4A/√3
 s²=(4x270.633 cm²)/4
 s²=625 cm²
 s=√625 cm²
 s=25 cm
 2. Now, you can find the radius (r) of the circle by applying the following formula:
 r=s/√3
 s is the side of the triangle
 3. Therefore, you have:
 r=25 cm/√3
 r=14.43 cm
 4. As you can see, the answer is:
 r=14.43 cm