The floor of a canyon has an elevation of −14.5 feet. Erosion causes the elevation to change by −1.5 feet per year. How many years will it take for the canyon floor to have an elevation of −31 feet?
The difference between the levels is 16.5, And feet/year is -1.5, So 16.5/-1.5 is -11, but since we cannot have a negative number we take the absolute value for an answer of 10.