Chapter 9 - Basic Algebra - 9.2 Adding and Subtracting Signed Numbers - 9.2 Exercises - Page 638: 20

The temperatures in the interior may easily drop $-75°C$.

On Antarctic islands temperatures drop to $-15°C$ but interior drop another $60°C$. $$-15 + (-60) = -75°C$$ The temperatures in the interior may easily drop $-75°C$.