The following data were obtained for a falling$-$head permeability test:

Length of the soil sample $=120mm$

Diameter of soil sample $=60mm$

Area of the standpipe $=20m{m}^2$

$t=0,$ head difference $=500mm$

$t=6$min, head difference $=360mm$

Determine the hydraulic conductivity of the soil $(c\frac{m}{sec})$

What was the head difference at $t=5$min $?$