Students learn to solve word problems that involve comparing integers or integer operations, such as the following. The highest elevation is 200 feet, and the lowest elevation is -400 feet. What is the difference between the highest and lowest elevations? In the given problem, the difference between the elevations is 200 - (-400), or 200 + (+400), which simplifies to 600 feet. Note that "difference" is a key word for subtraction, while "net profit", "net change", etc., are key words for addition.