As shown in Figure $1,$ two sturts $(A$&$B)$ have been proposed to install

when excavating $4\mathrm{.}0m$ deep trench in a sandy soil deposit. The horizontal

spacing of struts is $2m.$ The force acting on strut $A$ is:

Figure $1$

$=$ Unit weigh $t$ of soil

$K_a=$ Rankine's active earth pressure coefficient

For Clay : $C=c_u$ and ${}^{\text{'}}=0$

$K_a=\frac{1-sin{}^{\text{'}}}{1+sin{}^{\text{'}}}$

Select correct answer:

a$)57\mathrm{.}1$kN

b$)69\mathrm{.}3$ kN

c$)104\mathrm{.}5$kN