160 km because 20 hours times 8 km per hour
By using two arbitrary points on the line, we can find the slope using the slope formula:

We'll use the points (0, 4) and (5, 1) for this.
1 - 4 / 5 - 0
-3 / 5
The slope of the line is -3/5.
Rectangle is length multiplied by breadth