Answer:
39 minutes
Step-by-step explanation:
In this problem we can see that there is a constant/flat rate charge of $4 on every first minute
we can model the cost for calls as
[tex]y= 4+0.25x------1[/tex]
where x is the number of extra minutes spent
given that y = $13.75
We can simply substitute our given values into the equation 1 above and solve for x
[tex]13.75= 4+0.25x\\\\13.75-4= 0.25x\\\\9.75=0.25x[/tex]
Divide both sides by 0.25 to find x
[tex]x= 9.75/0.25\\\\x=39[/tex]
