Nuh huh. 100 should be your answer.
100 divided by 10 gives 10.
See how it works:
\(\displaystyle 0.1(100) = 10\)
And from our two initial equations:
\(\displaystyle y_A = 0.22x + 25 = 0.22(100) + 25 = 47\)
\(\displaystyle y_B = 0.12x + 35 = 0.12(100) + 35 = 47\)
So anything longer than or equal to 100 minutes is your answer.
Here is the graph of the two lines:
The blue line represents the total cost that company A charges and the purple line represents the total cost that company B charges. You see that for the most part, the line for company B is above that of company A, meaning that for those minutes, company B is more expensive. The point where they meet is where they charge the same fee and as soon as the purple line goes blow the blue line, company B is charging less expensive fees.