$(19$ points$)$ The $7075-T6$ aluminum rod $AB$ is bonded to the cold rolled red brass rod BD$.$ Section $CD$ is hollow and has an inner diameter of $40$ mm $.$ Determine the angle of twist of point A relative to point D$.$

For $2$ points extra credit on Exam $2,$ calculate the maximum shear stress of the shaft.

${}_{\frac{A}{D}}=$

Extra Credit

${}_{\text{M}\text{a}\text{x}}=$

$(7075-$T$6$ Aluminum$)$: G$=28$ GPA

$($Red Brass cold rolled$)$: G$=44$ GPA