$\text { heights } h _ { a } = 42 \mathrm {~mm} \text { and } h _ { s } = 68 \mathrm {~mm} \text {, }$

$$\text { A composite beam of aluminum } \left( E _ { a } = 72 \mathrm { GPa } \right) \text { and steel } \left( E _ { s } = 190 \mathrm { GPa } \right) \text { has a width } b = 25 \mathrm {~mm} \text { and }$$ $\text { heights } h _ { a } = 42 \mathrm {~mm} \text { and } h _ { s } = 68 \mathrm {~mm} \text {, }$ , respectively. A bending moment is applied about the z axis resulting in a maximum stress in the aluminum of 55 MPa. The maximum stress in the steel is approximately: $\text { MPa. }$

A) $86 \mathrm { MPa }$
B) $90 \mathrm { MPa }$
C) $94 \mathrm { MPa }$
D) $98 \mathrm { MPa }$