Question 1125813
I will answer the question is when they are equal.
45.99+0.50x=49.99+0.40x, where x is the number of minutes
0.10x=4.00
x=40 minutes after 400 used, or 440 minutes altogether.

If there is an inequality, it will favor plan B after 440 minutes, because each additional minute is cheaper.

The cost is 45.99+(40*0.50)=$65.99
or
49.99+(0.40*40)=$65.99