(a)[1]
A harbour's water level is recorded. In the morning, it measures $5\text{ m}$. By afternoon, it is $-2\text{ m}$. Work out the difference between the morning level and the afternoon level.
(b)[1]
At midday, the temperature is $9^\circ\text{C}$. By midnight, it has fallen by $15.3^\circ\text{C}$. Calculate the temperature at midnight.