We want to find what integer represents the temperature change of the water in Emily's fish tank and what the water temperature was on Tuesday. We will do these things one at a time. Let's begin by taking a look at a graph that represents this situation.

From the graph, we can see that the temperature of the water in Emily's tank decreased by $3^{\circ}$ from Sunday to Monday. We can use a number line to represent this fact.

As we can see from the graph, $- 3$ is the integer that represents the temperature change of the water in the fish tank from Sunday to Monday. Now let's focus on finding the temperature of the water on Tuesday. From the exercise, we know that the temperature increased by $3^{\circ}$ on Tuesday. Let's mark this on our number line

Notice that $- 3$ and $3$ are opposites. That means their sum equals $0 .$ Because of this, we can say that the temperature increase and decrease combine to make $0$ and that the temperature did not change overall between Sunday and Tuesday. The temperature of the water in Emily's fish tank on Tuesday is $7 8^{\circ} F .$

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