SOLUTION:
Where c is the cost and m is the number of minutes of phone use in a month
Plan A;
c = 9m
Plan B;
c = 8.6 + 7m
The amounts of monthly phone use that will make Plan A cost be at least as much as Plan B.
[tex]\begin{gathered} \text{Plan A }\ge\text{ Plan B} \\ 9m\text{ }\ge\text{ 8.6 + 7m} \\ 9m\text{ - 7m }\ge8.6 \\ 2m\text{ }\ge\text{ 8.6} \\ m\text{ }\ge\text{ }\frac{8.6}{2} \\ \\ m\text{ }\ge\text{ 4.3 minutes} \end{gathered}[/tex]
