$-$ P $8\mathrm{.}10$: At a point in a two$-$dimensional stress system, the known stress are shown in the Figure. Determine the principal stresses, maximum shear stress, and the angle $\backslash (\backslash$alpha $\backslash ).$

answer should be $-20.\mathrm{.}5$ rads and $178\mathrm{.}12$ stress please