please explain steps. thanks!

$2\mathrm{.}5$ The microsensor of Figure $2\mathrm{.}39($a$)$ consisting of two identical beams and a central rigid link is redesigned into the one of Figure $2\mathrm{.}39($b$).$ Consider that the two rigid pushrods in Figure $2\mathrm{.}39($b$)$ are attached to the corresponding identical bridges and the central link. The stiffness of the

FIGURE $2\mathrm{.}39$

Micromechanism With Rigid Link and $($a$)$ Two Beams and $($b$)$ Six Beams.

modified design is five $(5)$ times larger than the original design stiffness in the indicated motion direction. Express the length $l_2$ in terms of $l_1$ using lumped$-$parameter stiffness modeling and considering that all beam segments have identical cross sections and material properties.