The 10 -mm-diameter steel bolt is surrounded by a bronze sleeve. The outer diameter of this sleeve is $20 \mathrm{mm},$ and its inner diameter is $10 \mathrm{mm}$. If the bolt is subjected to a compressive force of $P=20 \mathrm{kN}$, determine the average normal stress in the steel and the bronze. $E_{\mathrm{st}}=200 \mathrm{GPa}, E_{\mathrm{br}}=100 \mathrm{GPa}$