Kapag radius 3.14 times the radius times radius
kapag diameter 3.14 times diameter

To find the area of a sphere or circle is to follow the formula 

but if the given is the diameter you'll just have to divide the diameter by 2 and follow the formula 

for example : (the given is diameter)
   the diameter is 12 divide it 2 and the multiply the ans. by itself so 6x6 = 36
then multiply by the pi or 3.14 and you'll get an answer of 113.04

and if the given is the radius
  for example the radius is 4 you'll just directly follow the formula
 4x4 = 16 , 3.14 x 16 you'll get an answer of 50.24