The phone company charges 10 cents to connect a call for one minute and 8 cents per minute after that.
We call x minute to talk after the first minute.
We have 10+8x≤100 (cents)
and 8x≤100-10
or 8x≤90 and x≤90:8
and x≤11.25
So: How long could you talk on the phone for 1 dollar: it is 11 minute and 15 seconds