An air bubble in a glass slab of refractive index 1.5 is 6cm eep as viewed from one face and 4cm deeo as viewed from the nother face. What is the thickness of the glass slab?

here

thickness of the slab = real depth from one face (d) + real depth from the opposite face (d')

now, we know that

refractive index = real depth / apparent depth

thus, for the one face

1.5 = d / 6cm

or

d = 9cm

and for the opposite face

1.5 = d'/4cm

or

d' = 6 cm

so, total thickness of the slab will be

T = d + d' = 9cm + 6cm

or

 T = 15 cm