Question 182839
.
Let x = number of minutes after the first 3 mins
then they already provide:
f(x) = 2 + 0.30x
where f(x) is the cost

Since he only have $5.60 to spend:
5.60 >= 2 + 0.30x
3.60 >= 0.30x
12 minutes >= x

Read: 
x has to to "less than or equal" to 12 minutes

Since x is the minutes AFTER the first 3 then
maximum total time <= 12+3 
maximum total time <= 15 minutes