What is the rate of change of the total cost in dollars with respect to the number of additional minutes?

What is the slope of the line that passes through the points (10, 18) and (−5, −12)?

Which value best represents the rate of change of the volume of water in the fish tank with respect to time?

The slope of the graph is $$\frac{1}{2}$$ .

A line is graphed on a coordinate grid.  Which statement best describes the line?

Which value represents the rate of change of y with respect to x for this function? 

$$\frac{2}{5}x-\frac{4}{7}y=\frac{3}{2}$$