Heat And Thermodynamics

A circular copper ring at $30^{\circ} \mathrm{C}$ has a hole with an area of $9.98 \mathrm{~cm}^2$. It is made to slip onto a steel rod of cross-sectional area of $10 \mathrm{~cm}^2$, by raising the temperature of both ring and rod simultaneously by an amount $\Delta T$. If the coefficient of linear expansion of copper and steel are $17 \times 10^{-6} \rho \mathrm{C}$ and $11 \times 10^{-6} \rho \mathrm{C}$, then minimum value of $\Delta T$ should be