How do you find the slope of a line?

-- Pick any small piece of the line.

-- From the left end to the right end of that piece, measure
how much the line rises or drops.

-- Measure how much horizontal distance that piece covers.

-- Divide the amount of rise or drop by the horizontal distance.
That number is the slope of the line.

-- If the line drops as it goes from left to right, then the slope is negative.