You can
put this solution on YOUR website!Plan A:
$25
Plan B:
Number of calls=n
$13+$0.06*n
Plan B will cost more than Plan A when $13+$0.06*n>$25
$13+$0.06*n>$25
-13 from both sides
$0.06*n>$12
/$0.06 from both sides
n>200
Plan A will be cost less when your number of calls is more than 200 (so 201 or more)