The rails of a railroad track are welded together at their ends (to form continuous rails and thus eliminate the clacking sound of the wheels) when the temperature is 60°F. What compressive stress s is produced in the rails when they are heated by the sun to 120°F if the coefficient of thermal expansion a = 6.5 X 10^-6 /F and the modulus of elasticity E = 30 X 10⁶ psi?