The cost of telephone plan for one minute is 0.10 dollars.

The total cost of telephone plan must be a multiple of 0.10 dollars, so the graph will be the graph of a step function.

If the time spent on talking is greater than 0 minutes, but less than or equal to 1 minute, then the cost of telephone plan is 0.10 dollars.

If the time is greater than 1 minute, but less than or equal to 2 minutes, then the cost of telephone plan is dollars.

The cost of telephone plan for 3 minutes is dollars, and so on.

Therefore equation for the total the cost of telephone plan for x minutes is .

Use the pattern of times and cost to make a table, where x is the number of minutes and C(x) is the total cost of telephone plan.

To draw the step function follow the steps.

1. Draw a coordinate plane.

2. Plot the points on the coordinate plane.

3. Then sketch the line segments, connecting the every two points (one dot point and one circle point) with a smooth line.

Note: A dot means that the point is include in the graph and a circle means that the point is not included in the graph.

From graph, the cost of telephone plan for 9 minutes 40 seconds (since ) is 1 dollars.

The cost of telephone plan for 9 minutes 40 seconds (since ) is dollars.

The call cost would be a that lasts 9 minutes 40 seconds 1 dollars.