If one cellphone company charges 5 per month plus .10 per min and another company charges 8 per month plus .7 per minute at which minute will they both cost the same?

If one cellphone company charges 5 per month plus .10 per min and another company charges 8 per month plus .7 per minute at which minute will they both cost the same?
Assuming that the .7 should have been .07 then 100 minutes, otherwise never.