Given the function defined in the table below, find the average rate of change, in simplest form, of the function over the interval 1\le x \le 31≤x≤3.

One cell phone plan charges $20 per month plus $0.15 per minute used. a second cell phone plan charges $35 per month plus $0.10 per minute used. write and solve an equation to find the number of minutes you must talk to have the same cost for both calling plans.