a) To get this, we have to get the value for each plan at 60 minutes
What we have to do here is to come to the x-axis and get the point at which we have 60 minutes
Then we trace it up and see the point at which it touches the blue line and the red line
The term 60 minutes is between 40 minutes and 80 minutes. Then we draw a line through this point on the x-axis and look at the point at which it touches the graphs (then we trace this point to the y-axis to get the exact y-coordinate cost values)
We can see that the line touches the blue line at $6 and for the red line, we can see it at $12
Plan B is the red line and thus, it costs more. To have the difference in price, we make a subtraction and we have $12 - $6 = $6
Thus, Plan B costs $6 more
b) What we have to do here is to get the point at which the two graphs crosses
At the point in which they cross, we can trace it to the x-axis
By doing this, we can see the tracing at 160 minutes
From this point onwards, we can see that the graph of Plan A (the blue line) shoots up than the red line. This means Plan A costs more than Plan B from this point