The slope of a line is calculated by dividing the one y portion of the line by one x portion of the line. In this problem we have two points which can indicate us one portion of the y axis and one portion of the x axis. If we have two points of one line, then we can calculate its slope:
Point one (x1, y1)
Point two (x2, y2)
then the slope can be calculated as:
m = (y2 - y1)/(x2 - x1)
So lets use our data:
Point one (2, 10)
Point two (5, 8)
then the slope can be calculated as:
m = (8 - 10)/(5 - 2)
m = -2/3
therefore the slope is negative and is -2/3