A centric load $\mathbf{P}$ must be supported by the steel bar $A B$. Using allowable stress design, determine the smallest dimension $d$ of the cross section that can be used when $(a) P=108 \mathrm{kN},(b) P=$ $166 \mathrm{kN} .$ Use $\sigma_{Y}=250 \mathrm{MPa}$ and $E=200 \mathrm{GPa}$.