Solving a problem in physics section 30 point 77 molecu

77. The French physicist Jean Perrin, observing under the microscope the change in concentration of suspended in water (ρ = 1 g / cm3) balls Gamboge (ρ1 = 1,25 g / cm3) with a change in altitude experimentally determined Avogadro constant. Define this value if the slurry temperature T = 298 K, the radius of the balls r = 0,21 m and the distance between the two layers 30 microns Δh = the number of beads in a single layer Gamboge two times greater than the other.