Note that a change can be an Increase or a decrease. For an Increase, use a positive number. For a decrease, use a negative number. \( \begin{array}{l}\text { (a) A tram moved upward } 9 \text { meters per second for } 72 \text { seconds. What was the total change in the } \\ \text { tram's elevation? } \\ \text { (b) In a lab, a substance was cooled by } 20^{\circ} \mathrm{C} \text { over a period of } 10 \text { hours at a constant rate. What } \\ \text { was the change in temperature each hour? } \\ \square{ }^{\circ} \mathrm{C}\end{array} \)

The total change in the tram's elevation can be found by multiplying its speed by the time it moved. So, if the tram moved upward at 9 meters per second for 72 seconds, the total change in elevation is \(9 \times 72 = 648\) meters. Therefore, the total change in elevation is +648 meters. For the cooling substance, when it cooled down by 20°C over 10 hours, you can determine the hourly change by dividing the total change by the time taken. Hence, the change in temperature each hour is \( \frac{-20}{10} = -2 \) degrees Celsius. So, the change in temperature per hour is -2°C.