An iron ball of diameter 6cm and is 0.1mm too large to pass through a hole in a brass plate when the ball and plate are at a temperature of ${20}^0\mathrm{C}$. The temperature (in ${}^{0}C)$ at which (both for ball and plate) the ball just pass through the hole is

$\left({\mathrm{\alpha }}_{\mathrm{iron}}=12\times {10}^{-6}/ {}^0\mathrm{C}, {\mathrm{\alpha }}_{\mathrm{brass}}=18\times {10}^{-6}/ {}^0\mathrm{C}\right)$