DECIDING WHETHER A FUNCTION IS INCREASING, DECREASING, OR CONSTANT
Some recent studies suggest that a teenager sends an average of 60 texts per day.[2] For each of the following scenarios, find the linear function that describes the relationship between the input value and the output value. Then, determine whether the graph of the function is increasing, decreasing, or constant.

The total number of texts a teen sends is considered a function of time in days. The input is the number of days, and output is the total number of texts sent.

A teen has a limit of 500 texts per month in his or her data plan. The input is the number of days, and output is the total number of texts remaining for the month.

A teen has an unlimited number of texts in his or her data plan for a cost of $50 per month. The input is the number of days, and output is the total cost of texting each month.