Answer:
diameter = 12 cm
radius = 6cm
circumference = 12
 cm ≈ 37.68 cm
 cm ≈ 37.68 cm
area = 36
 cm² ≈ 113.04 cm²
 cm² ≈ 113.04 cm²
Explanation:
r = radius
d = diameter 
C = circumference
A = area
The diagram shows a circle with a diameter of 12 cm
Diameter
d = 12 cm
Radius
 r = d/2
⇒ r = 12/2 
⇒ r = 6 cm
Circumference
 C = 
 d
d
⇒ C = 12
 cm
 cm
Area
A = 
 r²
r²
⇒ A = 
 x 6²
 x 6²
⇒ A = 36
 cm²
 cm²
If you use 
 = 3.14 then:
 = 3.14 then:
C = 37.68 cm
A = 113.04 cm²