From what I know about slopes, I'm pretty sure that's the path you have to take is the picture below.
For each box, you have to do is count the change in the y-value and the change in the x-value between the points. Once you know those values, you have to divide y by x.
For example, take a look at the first graph. If you count, the change in the y-value is 3 units. The change in the x-value is 5 units. So, since slope is y/x, the slope is 3/5, which would take us to graph to the left.
Don't be afraid to ask any questions! Hope this helped.
Edit: Oh, and for the graphs that have lines that are completely vertical, the slope is undefined. For the graphs with lines that are completely horizontal, the slope is 0.
ANSWER: The size of a red blood cell IS approximately half the size of a plant cell.
EXPLANATION:
<em>1. We divide the size of the plant cell by 2 to see if half of its size is the size of a red blood cell. </em>
Therefore, half of a plant cell's size is 0.000006325 m.
<em>2. We now compare the size of half of the plant cell to the size of the red blood cell.</em>
0.000006325 m and 0.000007 m are very close in size; therefore, the size of a red blood cell IS approximately half of a plant cell.