Question 898953
The problem just does not seem to  describe enough information.  Here is attempt to work with what you have:


Promotion:
{{{15+0.05*t}}} using t for minutes


Bill for the Promotion:
66


That $66 bill would be  {{{15+0.05t=66}}}.

Not known if the deal is for a month or a year or some other time period.  Still the bill was $66.

Solve that bill equation for t, the number of minutes.
{{{0.05t=66-15}}}
{{{0.05t=51}}}
{{{t=20*51}}}
{{{highlight(t=1020)}}} minutes, which is 17 hours.