Question $3[8$ marks$]$ Composite beam problem

Drawing: $3$ marks; Step wise solving: $2$ marks; Correct Moment of Inertia and Neutral axis location: $2$ marks; Results accuracy: $1$ mark.

Using the transformation principle, determine the maximum bending stress in each of the two materials for the composite section as shown below. When subjected to sagging the bending moment is of $50$ kN $-$m magnitude. Take Youngs modulus of Steel and aluminium as $210$GPa and $70$GPa respectively.