B 13 The Teleconnect telecommunications company has a variable call charge rate for phone calls of up to 30 minutes. The charges are 50c/min for the first 10 minutes, 75c/min for the second 10 minutes
and $1/min for the third 10 minutes.
Connectplus, a rival telecommunications company, charges a constant call rate of 60c/minute. What is the length of phone call for which both companies would charge the same amount?