The natural length of a spring is $3.0\,\text{cm}$. If a force of $60\,\text{N}$ is exerted on the spring, its length rises to $5.0\,\text{cm}$. The limit of proportionality is not exceeded. What is the spring constant of the spring?
- A$7.5\,\text{N cm}^{-1}$
- B$12\,\text{N cm}^{-1}$
- C$20\,\text{N cm}^{-1}$
- D$30\,\text{N cm}^{-1}$