Explanation:

3(2 πr2) = 2(2πrh)      [since  three times the sum of the areas of its two circular faces is twice the area of the curved surface area]

= 6πr2  = 4πrh

= 6πr2  / 4πr = h

= 3r/2 = 10.5 [since h = 10.5]

= r = 2*10.5/3 = 7cm

Therefore, the radius of the base is 7cm.

Hence, option 1 is the correct answer.