An object $(h_0=2\mathrm{.}0cm)$ is placed $25$ cm in front of the lens combination shown, with $f_2=+10\mathrm{.}0cm.$ The distance between the lenses is $15$ cm $,$ and an image is formed $17\mathrm{.}7$ cm behind lens $2.$ Calculate the focal length of the diverging lens.

$6\mathrm{.}1$ cm

$-15cm$

$12\mathrm{.}0$ cm

$-11\mathrm{.}8cm$