A trolley is kept stationary between two steel springs. Each spring begins with an unstretched length of $0.10\,\text{m}$. Spring P has spring constant $60\,\text{N m}^{-1}$. Spring Q has spring constant $120\,\text{N m}^{-1}$. The extension of spring P is $0.40\,\text{m}$. What is the extension of spring Q?
- A$0.10\,\text{m}$
- B$0.20\,\text{m}$
- C$0.30\,\text{m}$
- D$0.80\,\text{m}$