A spring of stiffness $\mathrm { k } = 15 \mathrm {~N} / \mathrm { m }$ is cut into a ratio of $3 : 1$. Find the spring constant of smaller length spring thus formed.\\
(A) $60 \mathrm {~N} / \mathrm { m }$\\
(B) $45 \mathrm {~N} / \mathrm { m }$\\
(C) $50 \mathrm {~N} / \mathrm { m }$\\
(D) $15 \mathrm {~N} / \mathrm { m }$