In a given linear equation, the value of the independent variable decreases at a constant rate while the value of the dependent variable increases at a constant rate. The slope of this line is

The slope is defined as the change in y/change in x ...

The y variable is the dependent variable, the x variable is the independent variable (you plug in values of x to get your y).

Given, the independent "x" change is increasing (or + ) and the dependent "y" change is decreasing (-),

your slope is: (-) / (+) = (-).

If they were both increasing ... (+) / (+)

or both decreasing (-) / (-)

the slope would be positive.