For a falling-head permeability test, the following are given:
Length of the soil specimen = 700 mm
Area of the soil specimen = 20 cm²
Area of the standpipe = 1.05 cm²
Head difference at time t = 0 is 800 mm
Head difference at time t = 8 min is 500 mm
a. Determine the absolute permeability of the soil.
b. What is the head difference at time t = 6 min?

Assume that the test was conducted at 20°C, and at 20°C, γ_ω= 9.789 kN/m³ and η = 1.005 X 10^-3 N ? s/m².