R$5-7.$ The solid segments $AB$ and $BC$ are made from $6061-$T$6$ aluminum and A$992$ steel, respectively. If the allowable shear

stresses are $({}_{\text{a}\text{l}\text{l}\text{o}\text{w}}{)}_{AB}=12$ksi and $({}_{\text{a}\text{l}\text{l}\text{o}\text{w}}{)}_{BC}=10$ksi, determine the maximum allowable couple forces $P$ that can be applied to the lever arm. The shaft is fixed at A and $C.$

Prob. R$5-7$