<u>Given</u>:
Given that the regular decagon has sides that are 8 cm long.
We need to determine the area of the regular decagon.
<u>Area of the regular decagon:</u>
The area of the regular decagon can be determined using the formula,
where s is the length of the side and n is the number of sides.
Substituting s = 8 and n = 10, we get;
Simplifying, we get;
Rounding off to the nearest whole number, we get;
Thus, the area of the regular decagon is 642 cm²
Hence, Option B is the correct answer.