You have the diameter of the circle is:
d = 20 cm
In order to calculate the area of the circle, use the formula for the area:
A = π r²
where π = 3.14 and r is the radius.
The radius is one half of the diameter:
r = 20 cm/2 = 10 cm
Next, replace the values of π and r into the formula for the area:
A = (3.1415) (10 cm)² = 314.16 cm²
Hence, the area of the circle is 314.16 cm²