A cantilever of length $l$, and flexural rigidity $EI$, stiffened by a spring of stiffness $k$, is loaded by a transverse force $P$, as shown.

The transverse deflection under the load is

1. $\dfrac{Pl^3}{3EI} \begin{bmatrix} \dfrac{3EI}{3EI+2kl^3} \end{bmatrix}$
2. $\dfrac{Pl^3}{3EI} \begin{bmatrix} \dfrac{6EI-kl^3}{6EI} \end{bmatrix}$
3. $\dfrac{Pl^3}{3EI} \begin{bmatrix} \dfrac{3EI-kl^3}{3EI} \end{bmatrix}$
4. $\dfrac{Pl^3}{3EI} \begin{bmatrix} \dfrac{3EI}{3EI+kl^3} \end{bmatrix}$