Physics Question on Ray optics and optical instruments

Question

As shown in the figure, a combination of a thin plano concave lens and a thin plano convex lens is used to image an object placed at infinity The radius of curvature of both the lenses is $30 \,cm$ and refraction index of the material for both the lenses is $175$ Both the lenses are placed at distance of $40 \,cm$ from each other Due to the combination, the image of the object is formed at distance $x=$ __ $cm$ , from concave lens.
shown in the figure, a combination of a thin plano concave lens and a thin plano convex lens is used to image an object placed at infinity

Accepted Answer

The correct answer is 120.
f11=(1.75−1)(−301)
⇒f1=−40cm
f21=(1.75−1)(301)⇒f2=40cm
Image from L1 will be virtual and on the left of L1 at focal length 40cm. So the object for L2 will be 80cm from L2 which is 2f. Final image is formed at 80cm from L2 on the right.
So x=120