A soil deposit has three layers having same thickness each but the permeabilities of the layers are in the ratio of 1 : 2 : 4 from top to bottom. What is the ratio of average permeability in the horizontal direction to that in the vertical direction ?

• A. 7 : 2
• B. 14 : 6
• C. 28 : 24
• D. 49 : 36