Wire diameter mean coil diameter and number of turns of a closely – coiled steel spring are d, D and N respectively and stiffness of the spring is K, A second spring is made of same steel but with wire diameter mean coil diameter and number of turns 2d, 2D and 2N respectively. The stiffness of the new spring is
(a) K (b) 2K (c) 4K (d) 8K