A metal rod with a Young's modulus y=2×10¹² dynecm⁻² and a coefficient of linear expansion α=1.6×10⁻⁵ per °C has its temperature raised by 20°C. The linear compressive stress to prevent the expansion is:
a) 3.2×10⁷ dynecm⁻²
b) 3.2×10⁶ dynecm⁻²
c) 3.2×10⁵ dynecm⁻²
d) 3.2×10⁴ dynecm⁻²