
Using Lens Makers formula for the plano-concave part, we can write
f11=(1.75−1)(−301)
⇒f1=−40cm
Using Lens Makers formula for the plano-convex part, we can write
f21=(1.75−1)(301)⇒f2=40cm
Image from first lens will be virtual and on the left of first lens at focal length 40cm. So the object for second lens will be 80cm from second lens which is 2f2. Final image is formed at 80cm from second lens on the right.
So, x=120.
