I've found the following question on IsaacPhysics.org . I've been working on it for a couple of hours but I cannot figure it out.
A looking glass is used to read an ancient scroll. This lens has a hemispherical shape with radius R and its flat surface is placed on top of the scroll being examined. The lens is made of glass of refractive index n. The reader is a distance h from the scroll along the axis of symmetry.
What is the minimum value of h for which the entire circular area of the scroll directly under the lens is visible to the observer if $R=3.70\ \rm cm$ and $n=1.30$?