The three springs are placed one above another in a vertical line, as illustrated. Springs $P$ and $Q$ are the same and each has spring constant $k$. Spring $R$ has spring constant $3k$. When a force $W$ is applied as shown, by how much does the total length of the arrangement increase?
- A$\frac{5W}{6k}$
- B$\frac{4W}{3k}$
- C$\frac{7}{2}kW$
- D$4kW$