While removing a wheel to change a tire, a driver applies forces $P=100 \mathrm{N}$ at the ends of two of the arms of a lug wrench (see figure). The wrench is made of steel with shear modulus of elasticity $G=78$ GPa. Each arm of the wrench is $255 \mathrm{mm}$ long and has a solid circular cross section of diameter $d=12 \mathrm{mm}$
(a) Determine the maximum shear stress in the arm that is turning the lug nut $(\operatorname{arm} A)$
(b) Determine the angle of twist (in degrees) of this
same arm.