$($Concrete elastic modulus Ec $=25,000$ Mpa, rebar elastic modulus Es $=2000000$ Mpa, and the elastic modulus ratio n$=$Es$/$Ec $=8$ can replace rebar with equivalent concrete area nAs$)$Reinforcing bars with a total cross$-$sectional area of As$=2$x$200=400$mm$^2$ were distributed at an effective depth of d$=500$mm on a reinforced concrete beam section with a width of b$=300$mm and a depth of $600$mm$.$ When the bending moment M$=50$kNm acts,$1.$ In a crack section, the neutral axis is formed at the point where compression and tension are shifted, i$.$e$.,$ where the crack stops occurring. Find the depth of the neutral axis of the crack section.$($Hint: No concrete in the area with cracks in the cross section is considered to be present$)2.$ Find a cross$-$sectional secondary moment with the neutral axis as the reference axis. $($Hint: When using the parallel axis theorem, you can ignore the cross$-$sectional secondary moment of the reinforcement.$)3.$ Find the vertical stress of a compression bridge and the vertical stress of a reinforcing bar caused by a bending moment$4.$ When the yield strength of the rebar is $400$ Mpa, determine if the rebar is yield.Fig. $3$