$6\mathrm{.}6)$ For the falling$-$head permeability test, the following are given:

Length of the soil specimen $=15$ in

Area of the soil specimen $=3$ in $2$

Area of the standpipe $=0\mathrm{.}15$ in$2$

Head difference at time $t=0$ is $25$ in

Head difference at time $t=8$min is $12$ in

A$.$ Determine the hydraulic conductivity of the soil $($in$/$min$)$

B$.$ What was the head difference at time $t=4$min $?$