Problem $2.(30$ points$)$

A doubly RC beam $200mm$ wide with an effective depth of $550mm$ is reinforced with $2$ No$.16$ diameter rebars in compression and two layers of No$.19$ diameter rebar $(3$ bars in each layer$)$ in tension. Calculate the depth of moment arms for the force of compression for both compression steel and concrete, also find the nominal moment of the beam section. Material properties are $f_y=420$MPa and $f_c^{\text{'}}=35$MPa.