First, determine 2 points on the graph. I'd recommend to choose 2 points that are next to each other to make it easier.
Second, see how many units higher the first point you chose (on the left) is than the second point you chose (on the right). Say it is 3 units, then you mark a points 3 units above the first point.
Third, see how many units to the right the second point is to the first. If it is 5 units, you would go to the point you marked on the previous step, and move 5 units to the right. If you did it correctly, it should end up on the second point you chose. The segment you drew should kind of look like a box.
Now, make a proportion. Put how many units you rose in the second step at the top, and how many you ran at the bottom. Treat this like a fraction and simplify. You have your slope!
Going higher and to the right is the formula rise/run. How many units do you rise, how many do you go right? I recommend doing this when finding slope on a graph
Hope I helped!!!!!!!!!!!!! :)
be the length of the rectangle and 
be the width. In the problem it is given that 
. It is also given that the area 
. Substituting in the length in terms of width, we have 
. Using the zero product property, 
. Solving these we get the width 
. However, it doesn't make sense for the width to be negative, so the width must be 
. From that we can tell the length 
.