Q$1.[10$ marks$]$

a$)$ Determine the location $\frac{?}{\text{b}\text{a}\text{r}}(y)$ of the centroidal axis $\stackrel{}{x}-\stackrel{}{x}$ of the beam's cross$-$sectional area, neglecting the dotted circle at center $N.($Note: Neglect the size of the corner welds at A and $B$ for the calculation.$)$

b$)$ If we want to set $\frac{?}{\text{b}\text{a}\text{r}}(y)=-130mm,$ determine the radius of the dotted circle to be drilled at center $N.$