Final answer:
To compare Plan A and Plan B for cost-effectiveness based on her expected phone usage, Tina should use the equations C = 49.95 + 0.05(m - 300) for Plan A and C = 39.95 + 0.10(m - 500) for Plan B, where 'C' is the total cost and 'm' is the number of minutes used.
Step-by-step explanation:
Tina is considering two cell phone plans and wants to find out which one will be the least costly based on her expected usage, assuming she always uses more than 500 minutes per month. To determine the cost of each plan, she can use two equations, one for each plan, including the monthly fee and the additional cost per minute beyond the included minutes.
For Plan A, which has a monthly fee of $49.95 and charges 5¢ per minute after 300 minutes of talk time, the cost equation would be C = 49.95 + 0.05(m - 300), where 'C' represents the total cost and 'm' represents the total minutes used.
For Plan B, with a monthly fee of $39.95 and a charge of 10¢ per minute after 500 minutes, the equation is C = 39.95 + 0.10(m - 500).
By comparing the two equations, Tina can determine which plan will be more cost-effective based on the number of minutes she plans to use.