Answer:
1st graph: m = -1/2. (m is the slope)
2nd graph: m = 3/2.
3rd graph: Midpoint = (1/2, 1/2)
Step-by-step explanation:
1st graph:
Find the slope by looking for two points on the line. Use the formula 
We can derive the points (-3, 0) and (1, -2). Plug these into the equation above.
Simplify this, giving you: m = -1/2.
2nd graph:
Use the same formula as stated above. From this graph, you can plug in the points (-1, 1) and (1, 4)
Simplifying gets you: m = 3/2.
3rd graph:
To find the midpoint, use the formula: 
Plug in the end-points of the graph, or (-3, 2) and (4, -1).
You get:
Simplify:
Midpoint = (1/2, 1/2)