Final answer:
The slope of the line with the equation 20-5x is -5, which is a negative value indicating a downward incline on the graph.
Step-by-step explanation:
The value of the slope of a line with the equation 20-5x can be determined by rearranging the equation into the slope-intercept form, which is y = mx + b, where m is the slope and b is the y-intercept. In this case, the equation can be interpreted as y = -5x + 20, which shows that the slope of the line is -5. The negative slope indicates that the line moves down the y-axis as the x-value increases. This slope value tells us that for every increase of 1 on the horizontal axis, there is a decrease of 5 on the vertical axis, signifying a relatively steep downward incline.