A stratified soil deposit has three layers of thickness z1 = 4, z2 = 1, z3 = 2 (units in m) and the corresponding permeability of k1 = 2, k2 = 1, k3 = 4 (units in m/s), respectively. The average permeability (in m/s units) perpendicular to the bedding planes will be:
1
16
2
8
3
2
4
4