$**$Exercise:$**$On the solid with a tetrahedral shape indicated in the following figure, a stress state has been caused by surface forces and body forces. The solution for the stresses is given as:$\backslash [\backslash$sigma$\_$x $=2$y $+$ z$,\backslash$quad $\backslash$sigma$\_$y $=-4$y $+2$z$,\backslash$quad $\backslash$sigma$\_$z $=-6$y $+3$z$\backslash ]\backslash [\backslash$tau$\_\{$xy$\}=-6$y $+2$z$,\backslash$quad $\backslash$tau$\_\{$xz$\}=\backslash$tau$\_\{$yz$\}=0\backslash ]$The stresses are expressed in N$/$cm$^2$ when $\backslash ($ x$,$ y$,$ z $\backslash )$ are measured in cm$.**$Required:$**1.$ Principal stresses and directions at point $\backslash ($ P$(2,1,3)\backslash )$ cm$\mathrm{.}2.$ Principal strains at the same point$\mathrm{.}3.$ Expressions for the surface forces on each face$\mathrm{.}4.$ Body forces.$**$Data:$**\backslash ($ E $=210\backslash )$ GPa, $\backslash ($

u $=0\mathrm{.}30\backslash ).$