#### Answer

a. The variables are Length and Time. They are inversely related.
b. The variables are Cost and Minutes of Calls. There is a period when the cost is constant for the minute of calls but then it increases at a constant rate.

#### Work Step by Step

For graph a, the independent variable is Time and the dependent variable is Board Length. The relation between the two variables is that as the time increases, the length of the board is decreasing.
For graph b, the independent variable is Minutes of Calls and the dependent variable is Cost. The relation between the two variables is that as the minute of calls increases, the cost increases at a constant rate but for the first few minutes of call the cost is the same as the slope of graph is 0, but then it increases at a constant rate after a certain minutes of calls.