A mercury thermometer was kept in ice (left(0^{circ} mathrm{C} ight)) for an indefinite period. It was removed

A mercury thermometer was kept in ice \(\left(0^{\circ} \mathrm{C}\right)\) for an indefinite period. It was removed and immediately put in boiling water \(\left(100^{\circ} \mathrm{C}\right)\). It showed \(75^{\circ} \mathrm{C}\) after 2.5 seconds. Evaluate transfer function of thermometer.