A railway track (made of iron) is laid in winter when the average temperature

A railway track (made of iron) is laid in winter when the average temperature is $18^{\circ} \mathrm{C}$. The track consists of sections of $12.0 \mathrm{~m}$ placed one after the other. How much gap should be left between two much sections so that there is no compression during summer when the maximum temperature goes to $48^{\circ} \mathrm{C}$ ? Co-efficient of linear expansion of iron=11 $\times 10^{-6} /{ }^{\circ} \mathrm{C}$.