Question

Find the surface area of a sphere of diameter: (i) 14 cm (ii) 21 cm (iii) 3.5 m

Answer 1

we know that 
The formula used for surface area of sphere is $4 \pi r^{2}$
so (1)14 cm
you know that diameter is 14 cm, now to find the radius(r) divide the diameter by 2.
so, r=7 cm
now,
       A=$4 \pi 7^{2}$
        A=$4 \pi ( 49)$
        A= $196 \pi cm^{2}$
(2)21 cm
      Radius=21/2=10.5
         A= $4 \pi (10.5)^{2}$
       A= $4 \pi (110.25)$
       A= 441  
(3) You have to convert the metre into centimetre and do the same procedure as done above.
The metre to centimetre value you will get is 350.
solve the rest.
Hope this helps