Help with Numerical Problem: Pointers Needed!

[pj96]

Homework Statement

Suppose that you focus a camera directly down on a letter printed on this page.
The letter is then covered with a 2.00-mm thick microscope slide (n = 1:55). By
how much must the camera be raised in order to keep the letter in focus?

Relevant Equations

Snell's law or refraction at a spherical interface?

I'm really stuck on this and have no solution only a numerical answer! Any pointers in the right direction would be really appreciated!

 

[BvU]

Hello pj, $\qquad$ $\qquad$ !

Unfortunately, according to the PF guidelines,

I'm really stuck on this and have no solution

does not count as an effort to try and find a solution. So we are not allowed to assist!

You could make a sketch of the two situations and that way discover what's different ...