What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm. Is the system a converging or a diverging less ? Ignore the thickness of the thickness of the lenses

Question

$\begin{array}{1 1} f=60\;cm ; converging \;lens \\ f=-60\;cm; converging \;lens \\ f=60 \;cm ; diverging \;lens \\ f=60\;cm ; diverging \;lens \end{array}$