See image below. A RC beam has overall depth $800$ mm $,$ width $400$ mm and clear concrete cover $40mm.fc\text{'}=40$MPa,$Ec=32\mathrm{.}8$GPa,$fsy=500$MPa and $Es=200$GPa. For deflection check, determine the neutral axis depth when the section is uncracked $($unit: mm $,$ round to a whole number$)$