An ink mark is made on a piece of paper. $A$ glass slab of thickness $t$ is placed on it. The ink mark appears to be raised up through a distance $x$ when viewed at nearly normal incidence. If the refractive index of the material of the glass slab is $\mu$,then the thickness of the glass slab $t$ is given by:

• A
  $\frac{(\mu-1)}{\mu x}$
• B
  $\frac{\mu x}{(\mu-1)}$
• C
  $\frac{(\mu-1) x}{\mu}$
• D
  $\frac{\mu}{(\mu-1) x}$