At midnight, the temperature in a city was \( 5 \) degrees Celsius. The temperature was dropping at a steady rate of \( 2 \) degrees Celsius per hour.
a. Write an inequality that represents \( t \) , the number of hours past midnight, when the temperature was colder than \( - 4 \) degrees Celsius. Explain or show your reasoning.
b. On the number line, show all the values of \( t \) that make your inequality true.