(a)[1]
The temperature inside Luke’s house is $18^{\circ}\text{C}$. The temperature outside his house is $-3^{\circ}\text{C}$. Find the difference between these temperatures.
(b)[1]
Luke’s thermometer measures temperature correct to the nearest degree. At midnight, it shows the temperature outside as $-6^{\circ}\text{C}$. Find the upper bound of the temperature outside at midnight.