A transparent rectangular tank contains two immiscible liquids at rest. The upper liquid layer has thickness 3d and index of refraction n_1 = 1.50, while the lower liquid layer has thickness 4d and index of refraction n_2 = 4/3. A small coin rests at the bottom of the tank directly beneath both liquid layers. An observer in air (n_air = 1.00) looks down at the coin from directly above along a line of sight nearly perpendicular to the upper liquid surface. What is the ratio of the coin's total apparent depth to its actual depth, d_apparent / d_actual?