A clock with a metallic pendulum is $5 \mathrm{s}$ fast everyday at a temperature of $20°\mathrm{C}$ and $10 \mathrm{s}$ slow at a temperature of $35°\mathrm{C}$. The coefficient of linear expansion of the metal of the pendulum is
 

A thin copper wire of length $l$ increases in length by $1\%$ if temperature is changed from ${\theta }_1$ to ${\theta }_2$. What will be the percentage increase of area of a thin copper plate of $2l\times l$ area at the same change of temperature?

A pendulum clock having copper rod keeps correct time at $20°\mathrm{C}$. It gains $15$ seconds per day if cooled to $0°\mathrm{C}$. The coefficient of linear expansion of copper is