Answer:
100 minutes
Step-by-step explanation:
Let
x ----> the number of minutes
y ----> the total cost of the plan
we know that
Cingular Plan
[tex]y=0.45x+39.99[/tex] -----> equation A
Verizon Plan
[tex]y=0.40x+44.99[/tex] -----> equation B
To find out how many additional minutes will it take for the two plans to cost the same
Solve the system of equations A and B
Solve by graphing
Remember that the solution is the intersection point both graphs
using a graphing tool
The solution is the point (100,84.99)
see the attached figure
therefore
For x=100 minutes
The cost for both plans is $84.99